CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 62/088,396, filed on December 5, 2014, the content of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] This disclosure generally relates to spectroscopy techniques and, more particularly, spectroscopy techniques for detecting components in a gas phase chemical mixture.

BACKGROUND

[0003] It is often desirable to detect components of a chemical mixture, including components that are present in the mixture as trace quantities. Various spectroscopic and non-spectroscopic techniques have been developed to address this need. In general, a mixture analysis technique exhibits two figures of merit: sensitivity and specificity. A highly sensitive technique can detect even a small quantity of a component in a mixture, whereas a highly specific technique can definitely identify a component even amid a highly complex background of other components in the mixture. An ideal technique would be both highly specific and highly sensitive.

[0004] Since the pioneering work of Balle and Flygare in the late 1970s, Fourier transform microwave ("FTMW") spectroscopy has provided a versatile and powerful tool for gas phase mixture analysis. FTMW spectroscopy of molecules larger than a few atoms typically relies on cold, highly supersaturated gasses, which can be provided by a pulsed, seeded supersonic jet or a buffer gas beam source. FTMW spectroscopy can provide identification of individual isotopomers within a mixture, and has superior abilities to definitively identify molecules within a complex mixture. On the other hand, the sensitivity of FTMW spectroscopy remains far behind ionization techniques, and, to date, other techniques such as gas chromatography-mass spectroscopy ("GCMS") and liquid chromatography-mass spectroscopy ("LCMS") are more widely used. With the exception of highly species-specific microwave-optical double resonance experiments, FTMW spectra are generally derived by amplifying and recording microwaves emitted by molecules. However, the small amount of energy (typically < 10 ^~4 eV) detected per molecule limits sensitivity.

[0005] It is against this background that a need arose to develop the embodiments described herein.

SUMMARY

[0006] Microwave spectroscopy, which identifies gas phase molecules via transitions between rotational quantum states of the molecules, can be highly specific, including chiral specificity, but typically has limits of detection in the 1 in 50,000 range or worse. Mass spectroscopy, which ionizes molecules and then measures a charge-to-mass ratio of resulting ions and fragments, can be highly sensitive (in the 10 ¹² range) but alone typically provides limited specificity. Some embodiments of this disclosure are directed to a combined spectroscopy technique, using elements from microwave spectroscopy, Moire deflectometry, and mass spectroscopy, to realize an improved apparatus that exhibits both high specificity and high sensitivity.

[0007] In some embodiments, an improved apparatus can produce a molecular beam containing a single rovibrational state or a few such states. This can be achieved by selecting a state from a cold, thermal molecular beam via a combination of Moire deflectometry and near-resonant microwave-induced forces. The spectroscopy technique can be applicable to a large class of polyatomic, polar molecules. Applications of such a beam, including sensitive, high-resolution microwave spectrometry and chiral purification through generation of enantiomer-selected beams from racemic sources, are presented in this disclosure. In addition, extensions of Moire deflectometry to realize beams of molecules in hyperpolarized nuclear magnetic states, readout-free nuclear magnetic resonance ("NMR"), and high-sensitivity gas phase infrared spectroscopy are presented in this disclosure.

[0008] In some embodiments, an apparatus includes: (1) a series of gratings configured to block ballistic trajectories through the gratings; (2) an analyte gas source positioned upstream of the gratings, and configured to emit a beam of gas phase molecules; (3) a deflection field generator configured to apply a deflection field in a region of the gratings, the deflection field configured to selectively deflect a subset of the molecules to allow their transmission through the gratings; and (4) a detector positioned downstream of the gratings, and configured to detect transmitted molecules. [0009] In some embodiments, a number of the gratings is at least 3.

[0010] In some embodiments, the analyte gas source is configured to emit the beam of gas phase molecules having a flux of at least about 1 x 10 ¹⁵ molecules/second and a temperature below about 15 K.

[0011] In some embodiments, the deflection field generator is configured to apply a spatially non-uniform, oscillating electric field in the region of the gratings, the electric field having a frequency that is detuned by a non-zero amount D relative to a microwave resonance frequency of the subset of the molecules. In some embodiments, D is in a range of up to about ±50 MHz.

[0012] In some embodiments, the deflection field generator is configured to apply the electric field having a magnitude in a range of up to about 10 ⁵ V/m, and a frequency in a range from about 1 GHz to about 50 GHz.

[0013] In some embodiments, the deflection field generator includes a multi-wire transmission line and a voltage source coupled to the multi-wire transmission line.

[0014] In some embodiments, the detector is an ionization-based detector.

[0015] In some embodiments, the apparatus further includes a vacuum chamber within which the gratings are disposed, and the vacuum chamber is configured to maintain a pressure of about 10 ^"4 torr or less.

[0016] In some embodiments, the apparatus further includes an excitation field generator positioned between the analyte gas source and the gratings, and configured to apply an excitation field to selectively promote a given rotational state of the subset of the molecules.

[0017] In some embodiments, the apparatus further includes an excitation field generator positioned between the analyte gas source and the gratings, and configured to apply multiple excitation fields of different polarizations to selectively excite an enantiomer included in the beam of gas phase molecules.

[0018] In additional embodiments, an apparatus includes: (1) an analyte gas source; (2) a series of gratings positioned downstream of the analyte gas source; (3) an excitation field generator configured to apply an excitation field in a region between the analyte gas source and the gratings; (4) a deflection field generator configured to apply a deflection field in a region of the gratings; and (5) a detector positioned downstream of the gratings. [0019] In some embodiments, the analyte gas source is a supersonic pulsed jet or a buffer gas source.

[0020] In some embodiments, a number of the gratings is at least 3.

[0021] In some embodiments, an open area per grating is less than about 25%.

[0022] In some embodiments, the gratings are configured to block ballistic trajectories through the gratings.

[0023] In some embodiments, the excitation field generator is configured to apply a microwave or an infrared excitation field.

[0024] In some embodiments, the excitation field generator is configured to apply microwave fields of substantially orthogonal polarizations.

[0025] In some embodiments, the deflection field generator includes a microwave source.

[0026] In some embodiments, the detector is an ionization-based detector.

[0027] Other aspects and embodiments of this disclosure are also contemplated. The foregoing summary and the following detailed description are not meant to restrict the disclosure to any particular embodiment but are merely meant to describe some embodiments of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] For a better understanding of the nature and objects of some embodiments of this disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

[0029] Figure 1 : Moire deflectometry: A) a single-slit deflectometry configuration that realizes high force sensitivity at the cost of low signal. Molecules are passed through a series of 3 precisely aligned slits. The molecules in certain states are subjected to a small transverse force, shown as broad, vertical arrows. The alignment is adjusted so that substantially only molecules experiencing the transverse force (deflected trajectories) are selectively transmitted. B) A Moire deflectometer. The individual slits have been replaced by gratings of N slits each. As in A), the alignment of the third grating is adjusted such that substantially only molecules experiencing the transverse force are selectively transmitted. Assuming a diffuse molecular beam source that is larger than the gratings, the net flux transmitted is a factor of N ² higher than in A). [0030] Figure 2: Forces from near-resonant alternating current ("AC") electric fields. A) A two-wire transmission line with an electric field shown. The inset shows the calculated electric field for the proposed configuration (about 8 volts, about 1 mm diameter wires). High field seeking molecules are deflected towards electrodes, low field seeking molecules are deflected away from the electrodes, and unperturbed molecules are not deflected. The transmission line can be terminated to prevent reflections (termination not shown). B) An example level diagram, in this case for 1-2 propanediol, a representative chiral molecule. An applied microwave field is red-detuned about 20 MHz from the 16944.95 MHz | loi ^>→ |2i2> transition, using the notation |J, Ka, Kc>. Under these conditions, molecules in the | loi> state are high field seekers, molecules in the |2 ₁₂ > state are low field seekers, and other unconnected states are largely unperturbed. C) An acceleration in m s ^"2 for | loi>, |2 ₁₂ >, and unperturbed |Ooo> molecules. Substantially only selected molecules are perturbed.

[0031] Figure 3: A schematic of an apparatus to produce a cold, state-selected molecular beam from a cold, thermal, racemic beam source. While molecules are passing through a Moire deflectometer, the molecules are exposed to a spatially non-uniform microwave field generated by a two-wire transmission line, which runs substantially parallel to a direction of propagation of a beam.

[0032] Figure 4: Simulations of molecules deflected by a spatially non-uniform, near-resonant microwave field. A) Simulation of various tracks; about 2% of trajectories for molecules in a selected state are passed to a detector. Substantially no "off-resonant" molecules are passed. B) A magnified view of a trajectory from A), showing microwave- mediated deflection. Simulated experimental conditions: [non-chiral] benzonitrile, about 2 mm transmission line wire diameter, about ± 4 volts at about 2.74 GHz on the transmission line, about 2 micron wide slits with about 10 micron spacing between slits, and about 60 cm in total length along a lateral direction. Note that the y axis (transverse direction) is greatly magnified compared to the x axis (lateral direction).

[0033] Figure 5: Simulations of trajectories for non-deflected and deflected molecules for a three-grating Moire deflectometer. A) Adjustment of a transverse position of a third grating allows a beam to be normally off in the absence of a microwave field. B) Simulation of tracks subjected to a spatially non-uniform microwave field; about 5% of trajectories for molecules in a selected state are passed to a detector. [0034] Figure 6: A) An extension of the apparatus of Figure 3 which realizes a high resolution spectrometer. Adjustments in a frequency of an infrared or microwave field applied before a beam enters a deflectometer can produce large changes in a transmitted flux. Although the figure shows the first excitation field as a microwave field, an infrared field also is contemplated. In this case, the apparatus would yield a high-sensitivity infrared spectrometer. B) An extension of the apparatus of Figure 3 which realizes a chiral selector. The first excitation field in A) has been replaced by a combination of AC electric fields with x, y, and z polarizations. The phases of these fields are adjusted such that the fields selectively promote one enantiomer of a racemic beam into an excited state. These fields are shown in more detail in Figure 7. This state is selectively passed by the Moire deflectometer, realizing an enantiopure and state-selected beam.

[0035] Figure 7: Microwave fields to selectively promote one enantiomer to an excited rotational state. A) An example level structure and electric-dipole allowed transitions for 1-2 propanediol, a small chiral molecule. B) Applied fields, in x, y, and z polarizations. These fields can be applied simultaneously or sequentially, and are shown here sequentially for clarity. C) Simulated state populations for S- and R- 1 ,2 propanediol. S-propanediol is selectively promoted. A change in sign, or an adjustment of the phase by π, of any one of the applied fields shown in B) can select for R- 1,2 propanediol instead. The ability to switch which enantiomer is selected by an all-electric technique without altering other experimental parameters makes this technique attractive for ultra-high resolution spectroscopy on chiral molecules.

[0036] Figure 8: Two embodiments of an apparatus to select closed-shell molecules by their nuclear ntj state. A) A Moire deflectometer configured to pass either nuclear spin-up (mi = I) or nuclear spin down (mi = -I) molecules. Unlike a microwave- mediated apparatus of some embodiments, a magnitude of a transverse force here can be less than a force to deflect by an entire grating spacing. In this case, even imperfect momentum transfers (as would result, for example, from a non-uniform magnetic field gradient) can result in a polarized transmitted beam. B) An extension of the apparatus configured to observe nuclear magnetic resonance signals from gas phase samples in a substantially collision-free environment without traditional, insensitive NMR pickup coils. Atoms or molecules are first polarized (or hyperpolarized) by selectively passing either spin up or spin down molecules though a Moire deflectometer. These polarized molecules are then subjected to a substantially uniform magnetic field and a sequence of NMR pulses, and then selected again. A net transmission reflects a transfer function of the NMR pulses.

DETAILED DESCRIPTION

[0037] Moire deflectometry

[0038] State-selected beams can be realized by applying transverse, state dependent forces to a collimated molecular beam from a source 100, and such forces are typically small. A high force resolution is realized if the beam is passed through three narrow slits of a series of barriers 102, as shown in Figure 1A. The beam is highly collimated by the first two slits, such that a modest transverse force controls transmission of the beam through the third slit. This configuration provides high force-sensitivity, but the high collimation involved can reduce a resulting detection signal to undesirable levels.

[0039] As shown in an embodiment of Figure IB, a Moire deflectometer can provide both high force-sensitivity and a high flux. A beam from a source 104 is passed through a set of three (or more) aligned, micro-fabricated physical gratings 106. In this embodiment, the gratings 106 are substantially identical to one another, and are arranged with substantially equal spacings from one grating 106 to the next along a lateral direction. These gratings 106 can be precisely arranged to be substantially equally spaced and substantially parallel, and transverse (vertical) positions of the gratings 106 are adjusted such that substantially all molecules which pass the first two gratings 106 along ballistic trajectories are blocked by the third grating 106. For such precisely aligned gratings 106 with open area (corresponding to slits) of less than about 25%, contrast is about 100% - that is, substantially no ballistic trajectories can pass. The desired micron-scale precision for geometries of this embodiment is comparable to the constraint on visible light optics, and can be achieved using optical techniques, for example. The gratings 106 can be arranged along a transverse (vertical) direction, so that gravitational forces do not produce unwanted deflections in the sensitive (transverse) direction of the deflectometer.

[0040] A relatively small, transverse force exerted during free flight between the gratings 106 is enough such that deflected molecules (and substantially only deflected molecules) can be transmitted through the gratings 106. A net flux through such a configuration is typically a factor of about 20-50 times less than an unfiltered flux for a selected state, and, for typical configurations, scales as N ² compared to single-slit configurations as shown in Figure 1A, where N is the number of slits per grating. It is noted that the configuration of Figure IB exploits Moire effects. Similar configurations, and qualitatively similar signals, can be exhibited based on matter-wave interference effects, but the gratings 106 of Figure IB can be sized beyond a threshold to observe such interference effects.

[0041] Applying Moire deflectometry to spectroscopy

[0042] Some embodiments of this disclosure are directed to a combination of microwave spectroscopy and Moire deflectometry, which provides an apparatus (e.g., a spectrometer) that realizes benefits from both techniques: isotopomer-specific, mixture compatible, gas phase molecule identification, combined with ultra-sensitive detection of ionization techniques. In some embodiments, the resulting apparatus can provide at least equal specificity and far greater sensitivity than a conventional FTMW spectrometer.

[0043] Forces from microwaves

[0044] The motion of polar molecules can be manipulated via spatially nonuniform microwave fields. For molecules with relatively small rotational constants, including almost all polyatomic molecules, typical forces applied to molecules by strong fields are essentially non-resonant: an applied field thoroughly mixes rotational states of such molecules, substantially destroying any resonant nature (and thus state-selectivity) of the applied field. In order to keep the rotational states largely unperturbed, a quantity a = E-D _d i _po i B , where E is the applied electric field, D _&po is a molecular dipole moment, and B is a typical rotational constant for a molecule, should be much less than unity, such as no greater than about 10 ^"1 , no greater than about 10 ^"2 , no greater than about 10 ^"3 , or no greater than about 10 ^"4 . This in turn means that applied forces are relatively small: typical accelerations experienced by molecules are less than about 40 m s ^"1 , or a few g's, and, for typical beam configurations, a typical transverse energy delivered by a near-resonant microwave field is less than about 1 μΚ, such as no greater than about 0.99 μΚ, no greater than about 0.95 μΚ, no greater than about 0.9 μΚ, no greater than about 0.7 μΚ, no greater than about 0.5 μΚ, no greater than about 0.1 μΚ, or no greater than about 0.05 μΚ.

[0045] In some embodiments, a spatially non-uniform, near-resonant microwave field can be generated as a fringe field near a microwave transmission line, such as a two- wire (or two-electrode) transmission line 200 shown in an embodiment of Figure 2. Using such a "near field" can result in a far greater field intensity and field intensity gradient than is typically available with comparable power in a traveling wave field. Figure 2A shows the field produced by the transmission line 200 as a function of height (along a transverse or y direction) above the transmission line 200, and Figure 2B,C shows predicted forces (or accelerations) experienced by molecules of 1 -2 propanediol in various states.

[0046] In the design of the illustrated embodiment, a transverse momentum delivered by the spatially non-uniform microwave field can be significant for substantially only molecules in a selected state |J, Ka, Kc>, but may not be equal for all molecules in this state. The momentum imparted can depend on details of electrode geometry, details of a molecule's trajectory, and a projection of the molecule's angular momentum on a field axis nij. While careful design can mitigate some of this variability, a state-selected beam as proposed here can be realized despite this variation in momentum transfer. Specifically, the transverse momentum delivered to the molecules can be essentially random, but large enough to deflect the trajectory by one or more grating spacings. Under these conditions, a portion of the molecules in the selected state will be transmitted, while substantially all non-selected states in unperturbed trajectories are blocked. A microwave-assisted Moire deflectometer operating in this "uncontrolled" regime can have two characteristics compared to an ideal "controlled" deflectometer: a flux can be lower by a factor of about twice a grating transparency / (typically yielding a flux of about 0.4 of optimal), and both states deflected towards and away from electrodes are substantially equally transmitted. The proposed deflectometer therefore selects two states, connected by the near-resonant microwave field. These states would be | loi> and |2 ₁₂ > in the embodiment shown in Figure 2.

[0047] Figure 3 shows an embodiment of an apparatus 300 implemented as a spectrometer to produce state-selected beams and to perform detection of components of such state-selected beams. The apparatus 300 includes a Moire deflectometer, which is implemented as an arrangement of physical gratings 302 which selectively pass trajectories which are deflected from unperturbed, ballistic trajectories. In order to realize such trajectories, the apparatus 300 operates under high vacuum conditions, so collisions with background gas molecules are rare. Molecules in a spatially non-uniform, near-resonant microwave field are subjected to a force either towards or away from areas of high field. Such forces are typically weak, and, in some implementations, a force exerted by the microwave field is on the same order as a force exerted by earth's gravity. Despite this relatively weak force, the extreme sensitivity of Moire deflectometer to small deflections means that high contrast between selected molecules and unselected molecules can be achieved.

[0048] The apparatus 300 of Figure 3 includes the following components:

[0049] (1) A high flux source 304 of rotationally cold, gas phase, polar molecules emits a beam of such molecules. Examples of suitable analyte gas sources include supersonic pulsed jets and buffer gas sources, a suitable flux can be in a range of at least about 1 x 10 ¹³ molecules/second, at least about 5 x 10 ¹³ molecules/second, at least about 1 x 10 ¹⁴ molecules/ second, at least about 5 x 10 ¹⁴ molecules/second, at least about 1 x 10 ¹⁵ molecules/second, or at least about 5 x 10 ¹⁵ molecules/second, and a suitable temperature can be up to, or below, about 15 K, up to about 13 K, up to about 10 K, up to about 8 K, up to about 5 K, up to about 3 K, up to about 1.5 K, up to about 1 K, or up to about 0.5 K. For example, a supersonic pulsed jet of some implementations can provide a source flux of about 5 x 10 ¹⁵ molecules/second, and a source temperature of about 1.5 K, when averaged over time and assuming about 10 Hz repetition rate. As another example, a buffer gas source of some implementations can provide a slightly lower source flux of about 10 ¹⁵ molecules/second, and a slightly higher source temperature of about 5 K, but with a substantially lower forward velocity, which can allow for higher resolution or more compact apparatus. In some

-5/2

implementations, a signal can scale linearly with flux, and as T ^" ; that is, a higher flux and a colder source can yield a more prominent signal.

[0050] (2) A series of precisely micro-machined gratings 302 are arranged such that non-deflected molecules are blocked by at least one of the gratings 302. In some implementations, at least 3 of such gratings 302 are included to satisfy this condition, but more gratings also can be included to provide higher immunity to passage of non-selected molecules, such as a result of background gas collisions and stray fields. For example, the number of gratings, in general, can be 3 or more, 4 or more, 5 or more, or 6 or more. The gratings 302 are arranged such that substantially all ballistic (straight) trajectories are blocked by the gratings 302. Any ballistic molecule that passes through the first two gratings 302 are blocked by the third grating 302. In contrast, molecules with a resonance near a frequency of an applied microwave field are deflected and can pass through the third grating 302 into a detection region. A set of pumps (not shown) can be configured to remove any molecules which are blocked or scatter from the gratings 302. [0051] The gratings 302 can be formed of a variety of materials, and, in some implementations, the gratings 302 are formed of thin film silicon nitride, or another nitride or other insulating materials. The gratings 302 also can be formed of a metal or a metal alloy, such as copper, stainless steel, or gold. In general, the gratings 302 can be formed of the same material, or can be respectively formed of different materials. Examples of suitable dimensions of the gratings 302 include: (a) a slit width (along a transverse direction) in a range of up to about 10 micron ("μιη"), up to about 5 μιη, up to about 4 μιη, up to about 3 μιη, up to about 2 μιη, or about 1 μιη, and down to about 0.5 μιη, or down to about 0.1 μιη (b) a spacing between slits (along a transverse direction within a particular grating 302 and measured from a center of one slit to a center of an adjoining slit for periodically arranged slits) in a range of up to about 100 μιη, up to about 50 μιη, up to about 40 μιη, up to about 30 μιη, up to about 20 μιη, or about 10 μιη, and down to about 5 μιη, or down to about 1 μιη (c) an open area per grating 302 (corresponding to slits) of less than about 25%, such as in a range of up to about 23%, up to about 20%, up to about 18%, up to about 15%, up to about 13%, or up to about 10%, and down to about 8%, or down to about 5%, (d) a grating width (along a transverse direction) in a range of up to about 100 mm, up to about 50 mm, up to about 40 mm, up to about 30 mm, up to about 20 mm, or about 10 mm, and down to about 5 mm, or down to about 1 mm (for up to about 10 ⁴ slits/grating, up to about 5 x 10 ³ slits/grating, or about 10 ³ slits/grating), (e) a spacing between the gratings 302 (along a lateral direction) of up to about 200 cm, up to about 100 cm, up to about 80 cm, up to about 60 cm, up to about 40 cm, or about 20 cm, and down to about 10 cm, or down to about 1 cm, and (f) a total instrument length (or a total length of the Moire deflectometer) in a range of up to about 600 cm, up to about 300 cm, up to about 240 cm, up to about 180 cm, up to about 120 cm, up to about 60 cm, or smaller than about 60 cm, such as about 30 cm.

[0052] In some implementations, the slit width is less than about 25% of the spacing between slits. A desired deflection, and thus a desired field, can scale linearly with grating dimensions, and higher fields can result in lower resolution, as described above. It is therefore desirable, for some implementations, that the gratings 302 are configured as small as practicable. A lower limit of the grating dimensions can be set by molecular diffraction. For example, in the case of molecules of about 100 atomic mass unit ("AMU") and a velocity of about 500 m/sec, the gratings 302 can be configured to about 1 μιη slit width or larger, and about 5 μιη slit spacing or larger. In some implementations, the gratings 302 have dimensions that are substantially the same to one another and with substantially the same periodicity and spacing of slits, and the gratings 302 are arranged with substantially equal spacings from one grating 302 to the next along a lateral direction. In some implementations, the middle grating 302 is configured to have about half the slit-slit spacing, and therefore about twice the open area, as the first and third gratings 302. This arrangement can yield about the same contrast but about twice the flux. More generally, the middle grating 302 can be configured to have a reduced slit-slit spacing, and therefore a greater open area, as the first and third gratings 302.

[0053] (3) A deflection electric field generator 306, such as including an arrangement of electrodes, is configured to produce an oscillating, spatially non-uniform electric field in a region of the gratings 302. A two-wire transmission line 308 as shown in Figure 3, or other multi-wire transmission line, is an example of such arrangement, and a fringe field of the transmission line 308 at least partially overlaps the region between the gratings 302. An oscillating voltage source 310, such as including a microwave source and an amplifier, applies an oscillating voltage to the electrodes of the transmission line 308 at a frequency nearly resonant with a microwave transition in a component to be selected. Nearly resonant in this context means that the frequency of an applied electric field is detuned by a non-zero amount D, with D typically a few MHz, such as in a range of up to about ±100 MHz, up to about ±90 MHz, up to about ±80 MHz, up to about ±70 MHz, up to about ±60 MHz, up to about ±50 MHz, up to about ±40 MHz, up to about ±30 MHz, or up to about ±20 MHz, and down to about ±10 MHz, or down to about ±1 MHz. The dimensionless quantity E-Ddip _o i h can provide an estimate of a desirable amount of detuning, where E is the applied electric field, D^p _o i _e is a molecular dipole moment, and h is Plank's constant. For a typical polar molecule with about 2 Debye molecular dipole moment and an applied field of about 5000 V/m, this corresponds to a detuning of about 50 MHz in magnitude. More detailed numerical simulations can be performed and indicate that the desirable amount of detuning for these conditions is about 20 MHz in magnitude. This detuning can also be seen as a spectral resolution of the deflectometer, assuming no pre-excitation stage is included. Molecules of the component to be selected are either attracted to the electrodes or repelled, depending on the sign of D, and such deflected molecules can pass through all of the gratings 302 into the detection region. In some implementations, an applied field is red-detuned relative to a microwave resonance frequency, namely the sign of D is negative or the frequency of the applied field is smaller than the microwave resonance frequency by an amount corresponding to the magnitude of D. The magnitude of an applied field can be in a range of up to about 10 ⁵ V/m, up to about 5 x 10 ⁴ V/m, up to about 10 ⁴ V/m, or up to about 5 x 10 ³ V/m, and down to about 10 ² V/m, or down to about 10 V/m, and the frequency of the applied field can be in a range from about 0 GHz to about 50 GHz, or from about 1 GHz to about 50 GHz. In some implementations, another end of the transmission line 308 can be terminated with a resistor (not shown in Figure 3) to reduce reflections of a travelling microwave field.

[0054] (4) A detector 312 is positioned beyond the last (here, the third) grating 302, and is configured to detect transmitted molecules of a selected component that passes through the gratings 302. In some implementations, the detector 312 is an ionization-based detector, and includes an ionization element that ionizes transmitted molecules, and an ion counter that detects ionized molecules, such as a residual gas analyzer. In some implementations, a mass spectrometer, such as a quadrupole mass spectrometer, can be included as the detector 312. In such implementations, both a resonant frequency and a mass of a molecule can be detected, definitively identifying the molecule. Examples of suitable mechanisms of ionization include hot wire ionization, electron bombardment ionization, and laser ionization.

[0055] (5) A housing 314 is included within which at least some, or all, of the foregoing components are disposed. The housing 314 can be implemented as a vacuum chamber, within which vacuum conditions are maintained, such as through a set of pumps, to reduce background gas collisions, such as where typical molecules undergo significantly less than 1 collision per molecule as the molecules pass through the gratings 302, for example, on average no greater than about 1 collision per 10 molecules, no greater than about 1 collision per 10 ² molecules, no greater than about 1 collision per 10 ³ molecules, or no greater than about 1 collision per 10 ⁴ molecules. Suitable vacuum conditions can correspond to a pressure of about 10 ^"4 torr or less, about 5 x 10 ^{" 5} torr or less, about 10 ^"5 torr or less, or about 5 x 10 ^"6 torr or less. Different portions of the apparatus 300 can be maintained at different pressures in some implementations. For example, a pressure in a first portion of the apparatus 300 (upstream from the first grating 302) can be higher, such as about 5 x 10 ^"5 torr, than that of a second portion of the apparatus 300 (downstream from the first grating 302), such as about 10 ^"5 torr. [0056] The apparatus 300 also can include a controller (not shown in Figure 3) to direct operations of various components of the apparatus 300. Such a controller can be implemented in hardware, software, or a combination of hardware and software.

[0057] Figure 4 shows simulated trajectories for molecules from a supersonic jet for example experimental parameters of a three-grating Moire deflectometer. Here, about 2% of trajectories for molecules in a selected state are passed to a detector.

[0058] Figure 5 shows further simulated trajectories for non-deflected and deflected molecules for a three-grating Moire deflectometer. Here, about 5% of trajectories for molecules in a selected state are passed to a detector.

[0059] Extensions: High resolution spectrometry and chiral selectivity

[0060] Microwave-mediated deflectometry as a high resolution spectrometer

[0061] Although forces applied via nearly-resonant microwave fields can be highly state selective, field strengths to produce desired deflections can result in power broadening in a resultant microwave spectrum. For typical molecules in certain configurations of a spectrometer, broadening can be on the order of 10 MHz, greater than the order of 50 KHz resolution of low resolution FTMW spectrometers.

[0062] Figure 6A shows an embodiment of an apparatus 600 which allows for both high resolution and high sensitivity. Certain aspects of the apparatus 600 of Figure 6A can be implemented as similarly described for Figure 3, and those aspects are not repeated. The illustrated apparatus 600 of Figure 6A operates via the following sequence:

[0063] 1. Inject a gas mixture to be analyzed using an analyte gas source 604, such as a supersonic jet or a cryogenic buffer gas beam source, producing a cold molecular beam.

[0064] 2. Using a narrow band microwave or infrared excitation field from an excitation field generator 616, selectively promote a given rotational state of a given suspected mixture component to a previously thermally unoccupied, excited state |A>. If no such state is reachable via an interaction with a single field, multiple fields, including efficient state transfers via rapid adiabatic passage, can be applied.

[0065] 3. Allow the beam to pass into a Moire deflectometer, implemented as an arrangement of physical gratings 602 and configured such that substantially all ballistic (straight) trajectories are blocked. [0066] 4. While in the deflectometer and using a deflection electric field generator 606, subject the beam to a spatially non-uniform, nearly-resonant microwave field, tuned close to a transition between |A> and a second thermally unoccupied state |B>. Depending on the detuning D, molecules in state |A> will be deflected either towards or away from regions of high microwave intensity. A fraction of these molecules, and selectively these molecules, pass through the deflectometer into a detection region.

[0067] 5. Ionize and detect transmitted molecules with a sensitive, but nonspecific ionization mechanism of a detector 612, such hot filament or electron impact ionization. Undesired background counts can be dramatically reduced by selecting resultant ions for mass, for example, with a quadrupole mass spectrometer.

[0068] Small changes in a frequency of the excitation field used in operation 2 can result in large changes in a flux detected in operation 5, realizing a high resolution, high sensitivity spectrometer that can interrogate a single rovibrational state at a time. Further extensions can be implemented to interrogate multiple states simultaneously, which provides an advantage when analyzing previously uncharacterized samples.

[0069] Microwave-mediated deflectometry as a chiral selector

[0070] Figure 6B shows an embodiment of an apparatus 620 that realizes another extension of Figure 3 which filters a racemic beam of chiral molecules to realize a substantially enantiopure beam. Certain aspects of the apparatus 620 of Figure 6B can be implemented as similarly described for Figures 3 and 6A, and those aspects are not repeated. A high-resolution excitation field described in the above section has been replaced by multiple microwave excitation fields of different polarizations from an excitation field generator 622, here three microwave fields of mutually substantially orthogonal polarizations as shown in Figure 7, configured to selectively excite one enantiomer of a racemic sample. This is an extension of enantio-selective, microwave, three-wave mixing in chiral molecules, and can find use in various applications including state and enantiomer-s elected collision studies, high sensitivity chiral and species-specific chemical analysis via ionization detection, and enantio-purification applicable to species which racemize rapidly.

[0071] Embodiments of an apparatus of this disclosure can provide a combination of high sensitivity and high specificity. In some embodiments, sensitivity can be quantified as a limit of detection, amid a favorable background with one hour of measurement time. Detection limit can be taken as 95% confidence, or 2 sigma. Under these conditions, an apparatus of some embodiments can attain about 10 ⁶ counts/second for a pure sample, and about 5 background counts/second, resulting in a sensitivity of about 2 in 10 ⁷ . More generally, a sensitivity of the apparatus can be at least or greater than about 1 in 10 ⁵ , at least about 7 in 10 ⁶ , at least about 5 in 10 ⁶ , at least about 3 in 10 ⁶ , at least about 1 in 10 ⁶ , at least about 7 in 10 ⁷ , at least about 5 in 10 ⁷ , at least about 3 in 10 ⁷ , or at least about 1 in 10 ⁷ , compared to conventional microwave spectroscopy having a sensitivity of about 1 in 50,000 or worse.

[0072] In some embodiments, specificity can be quantified as follows: given an equal parts mixture of "random" chemicals A and B, what is a probability of misidentifying A as B, or failing to resolve the mixture. In order to yield this misidentification in a high resolution apparatus, A and B would have to have the same mass, or break into fragments of the same mass, and have the same three rotational constants each to about 1 part in 10 ⁴ . The probability of misidentification is about 10 ^"2 x 10 ^"4 x 10 ^"4 x 10 ^"4 , or about 10 ^"14 , which can be practically excluded as highly unlikely. The specificity realized without the high resolution extension can be lower, since the rotational constants can be measured to about 1 part in 100. In this case, the probability of misidentification would be about 10 ^"8 (or less), and highly complex mixtures can result in reduced specificities. For comparison, the same calculation for GCMS and LCMS yields a probability of misidentification of about 10 ^"5 .

[0073] Extension to other forces

[0074] Moire deflectometers can combine a large acceptance angle with high sensitivity to small forces. Such deflectometers, or related matter-wave interferometers, can be used to detect forces due to electrostatic polarizability of non-polar molecules, inertial forces such as gravity, and optical non-resonant photon-recoil forces, among others. Above, some embodiments are described in the context of using a Moire deflectometer in the presence of near-resonance, microwave- mediated forces. In the following, additional embodiments are described in the context of another small force: nuclear paramagnetism.

[0075] The Stern-Gerlach experiment separated silver atoms based on the interaction of their unpaired electron's spin with an external magnetic field. A closed-shell atom or molecule in a non-uniform magnetic field experiences a lower magnetic force than paramagnetic atoms or molecules with unpaired spins, but still in principle can be separated via a Stern-Gerlach-type experiment, provided the molecule contains at least one nucleus with nonzero spin. The high sensitivity of the Moire deflectometers of this disclosure makes them an attractive apparatus in which to realize such separation.

[0076] Figure 8A shows an embodiment of such an apparatus 800, which selects atoms or molecules based on a projection of a nuclear magnetic moment on a magnetic field axis mi. In the illustrated embodiment, the molecules exhibit two such states. This would be the case for certain small molecules, such as ¹³ C02, while many molecules exhibit higher total nuclear magnetic moments, typically dominated by spins from 1H atoms. The configuration of magnets 802 shown is the "asymmetric pole" permanent magnet used in a Stern-Gerlach-type experiment, but various other configurations, including a high-gradient Halbach array, are contemplated. In particular, a Halbach array can allow for both higher gradients and a larger transverse beam acceptance than the asymmetric pole configuration. Figure 8B shows an extension, in which two such mi filters or selectors 806 and 808 and an intermediate "NMR region" 810 are combined to realize an NMR apparatus 804. In this apparatus 804, polarized molecules passed by the first mi filter 806 enter the region 810 containing a substantially uniform magnetic field, in which the molecules can be driven by a series of NMR pulses. These pulses can leave the molecules in a likely distinct nuclear state, which can be read out by the second mi filter 808. It is noted that although the field in the NMR region 810 is substantially uniform in order to prevent or reduce dephasing, this field does not have to be of high magnitude.

[0077] In typical NMR experiments, samples are polarized via a typically small thermal polarization in a high magnetic field, and a final polarization is read out via detection of a small, oscillating magnetic field emitted by precessing nuclei. Here, the illustrated embodiment can achieve much higher polarizations through high-fidelity state filtering, and a comparatively insensitive detection can be replaced by ultra-sensitive ionization detection. The illustrated embodiment is a realization of NMR in a "clean" system: a gas phase sample in a substantially collision- free regime. Moreover, a combination of this technique with the ability to select specific rotational states as described above can allow for the direct observation of dipole-dipole terms that typically average to zero in un-oriented samples.

[0078] A magnitude of nuclear magnetic forces is typically much larger than those of microwave-mediated forces. For example, a spin-1 water molecule experiences a Zeeman shift of about 2 mK in a 1 Tesla field, compared with about 400 μΚ AC Stark shift for a highly polar benzonitrile molecule in a 10 V/cm AC electric field. It should also be noted that the second order Zeeman shift in closed shell molecules, which arises from their magnetic susceptibility, is in general much smaller than the first order nuclear shift for typical fields. For example, even at 5 Tesla the first order shift for mi = 1 magnetic states of water is more than about 20 times the second order shift experienced by mi = 0 nonmagnetic state. Magnetic susceptibilities vary modestly with gas, and so this result can be applicable for a wide range of smaller molecules.

[0079] An embodiment of this disclosure relates to a non-transitory computer- readable storage medium having computer code thereon for performing various computer- implemented operations. The term "computer-readable storage medium" is used herein to include any medium that is capable of storing or encoding a sequence of instructions or computer codes for performing the operations, methodologies, and techniques described herein. The media and computer code may be those specially designed and constructed for the purposes of an embodiment of this disclosure, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of computer-readable storage media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and execute program code, such as application-specific integrated circuits ("ASICs"), programmable logic devices ("PLDs"), and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher-level code that are executed by a computer using an interpreter or a compiler. For example, an embodiment may be implemented using Java, C++, or other object-oriented programming language and development tools. Additional examples of computer code include encrypted code and compressed code. Moreover, an embodiment may be downloaded as a computer program product, which may be transferred from a remote computer (e.g., a server computer) to a requesting computer (e.g., a client computer or a different server computer) via a transmission channel. Another embodiment may be implemented in hardwired circuitry in place of, or in combination with, machine-executable software instructions.

[0080] As used herein, the singular terms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise. [0081] As used herein, the term "set" refers to a collection of one or more objects. Thus, for example, a set of objects can include a single object or multiple objects. Objects of a set also can be referred to as members of the set. Objects of a set can be the same or different. In some instances, objects of a set can share one or more common characteristics.

[0082] As used herein, the terms "substantially," "substantial," and "about" are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. When used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. When used in conjunction with polarizations or orientations, "substantially orthogonal" can encompass a range of variation of less than or equal to ±10° relative to 90°, such as less than or equal to ±5°, less than or equal to ±4°, less than or equal to ±3°, less than or equal to ±2°, less than or equal to ±1°, less than or equal to ±0.5°, less than or equal to ±0.1°, or less than or equal to ±0.05°. When used in conjunction with two (or more) numerical values, "substantially the same," "substantially identical," or "substantially equal" can encompass a difference between the numerical values of less than or equal to ±10% of an average of the numerical values, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0083] As used herein, the terms "optional" and "optionally" mean that the subsequently described event or circumstance may or may not occur and that the description includes instances where the event or circumstance occurs and instances in which it does not.

[0084] Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual values such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth.

[0085] While the disclosure has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the disclosure as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the disclosure. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the disclosure.