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Near infrared absorption spectra of ethane (C2H6) were recorded in the 1800–6200 cm−1 region by high resolution Fourier transform spectroscopy (Bruker IFS 125 HR) at the Canadian Light Source (CLS). Absorption cross sections were obtained for pure samples and with nitrogen or hydrogen as broadening gases as appropriate for astronomical environments. Corrections to the cross sections were made using data from the Pacific Northwest National Laboratory (PNNL) infrared database.

Vibrational states of trans-acrolein (propenal) between 1020 and 1200 cm−1 are analyzed using high-resolution infrared spectra obtained at the Canadian Light Source synchrotron radiation facility. The one fundamental in this range, ν10 (C-C stretch vibration) is found to be strongly mixed with a combination vibration ν14 + ν18 by a Fermi-type interaction. Five additional states are directly observed via hot, combination, and overtone bands: ν11 + ν18, ν16 + ν18, ν15 + ν18, 2ν12, and 2ν17. These seven vibrational states are analyzed in a large multi-state fit, along with nine more states which are not directly observed but which affect the observed states by means of many perturbations. Though this fit is cumbersome, incomplete, and not unique, it can account for 3668 out of 3835 assigned lines with an average error of less than 0.0004 cm−1.

Using spectra obtained at the Canadian Light Source synchrotron radiation facility, a previously unobserved out-of-plane vibration of trans -acrolein (propenal) is reliably assigned for the first time. Its origin is at 1002.01 cm −1 , which is about 20 cm −1 higher than usually quoted in the past. This mode is thus labelled as v 14 , leaving the label v 15 for the known vibration at 992.66 cm −1 . Weak combination bands 17 1 18 2 ← 18 2 , 17 1 13 1 ← 13 1 , 12 1 18 2 ← 18 1 , and 17 1 18 2 ← 18 1 are studied for the first time, and assignments in the known v 11 , v 16 , and v 15 fundamental bands are also extended. The seven excited vibrations involved in these bands are analyzed, together with five more unobserved vibrations in the same region (850–1020 cm −1 ), in a large 12-state simultaneous fit which accounts for most of the many observed perturbations in the spectra.

The high-resolution rotationally resolved Fourier-transform infrared spectrum of the NO2 in-plane rock band (440–510 cm−1) of nitromethane (CH3NO2) has been recorded using the Far-Infrared Beamline at the Canadian Light Source, with a resolution of 0.00096 cm−1. About 1773 transitions reaching the upper state levels m ′ = 0 ; K a ′ ⩽ 7 ; J ′ ⩽ 50 have been assigned using an automated ground-state combination difference program together with the traditional Loomis–Wood approach. These data from the lowest torsional state, m′ = 0, were fit using the six-fold torsion-rotation program developed by Ilyushin et al. (2010). The analysis reveals that the rotational energy level structure in the upper vibrational state is similar to that of the ground vibrational state, but the sign and magnitude of high-order constants are significantly changed suggesting the presence of multiple perturbations.

The weak combination bands ν12 +ν18 and ν17 +ν18 of trans-acrolein in the 700-760cm-1 region are observed at high resolution (

Infrared Fourier transform spectra of the 12 CD 3 OH isotopologue of methanol recorded at the Canadian Light Source synchrotron have been investigated in the 750–950 cm −1 region to explore the torsional energy pattern of the in-plane methyl-rocking mode. The in-plane CD 3 -rocking band is primarily of parallel a -type character with relatively widely spaced K -structure, and the central Q -branch region is well-resolved. Sub-bands have been assigned for the v t = 0 ground torsional state from K = 0 to 15 for both A and E torsional species, as well as a number of sub-bands in the v t = 1 excited torsional state. A variety of perturbations due to asymmetry-induced, anharmonic Fermi and level-crossing resonances is seen in the spectra. Mapping of K -reduced torsional energies determined from the upper-state term values shows that the K -dependence is severely distorted from the usual pattern of smoothly oscillating, near-sinusoidal interlocking τ -curves. Although the K = 0 levels are nominally inverted for v t = 0, the torsional splitting is very small with the A level higher than the E level by only 0.625 cm −1 , and the anomalous behavior precludes a definite conclusion about torsional inversion. However, the range of variation with K of the v t = 0 CD 3 -rocking τ -curves is about half that of the ground vibrational state, similar to previous observations for CH 3 OH isotopologues, suggesting a comparable reduction of about 25% in the effective torsional barrier height for the in-plane rocking mode.

Quantum monodromy has a dramatic and defining impact on all those physical properties of chain-molecules that depend on a large-amplitude bending coordinate, including in particular the distribution of the ro-vibrational energy levels. As revealed by its pure rotational (a-type) spectrum [B. P. Winnewisser et al., Phys. Chem. Chem. Phys., 2010, 12, 8158-8189] cyanogen iso-thiocyanate, NCNCS, is a particularly illuminating exemplar of quantum monodromy: it clearly shows the distinctive monodromy-induced dislocation of the ro-vibrational energy level pattern for its low-lying bending mode. This dislocation centers on a lattice defect in the energy vs. momentum map of the ro-vibrational levels at the top of the barrier to linearity, and represents an example of an excited state quantum phase transition [D. Larese and F. Iachello, J. Mol. Struct., 2011, 1006, 611-628]. To complete the data, so far limited to ΔJ = +1 transitions, we decided to measure the high-resolution far-infrared band of the large-amplitude bending vibration ν7, and, if possible, mid-infrared bands. This Perspectives article presents our ongoing progress towards this goal, beginning with the description of how to predict line positions and intensities of the a- and b-type bands of the large amplitude bending mode using the Generalized-SemiRigid-Bender (GSRB) Hamiltonian for NCNCS and ab initio dipole moment functions [B. P. Winnewisser et al., Phys. Chem. Chem. Phys., 2010, 12, 8158-8189]. We include background information about synchrotron physics to clarify the advantages and limitations of that radiation source for our experiments. Details of the chemical preparation and sample handling, leading to the realization that NCNCS is 50 kJ mol(-1) lower in energy than its isomer S(CN)2 [Z. Kisiel et al., J. Phys. Chem. A, 2013, 117, 13815-13824] are included. We present the far-infrared and mid-infrared spectrum of NCNCS obtained at the Canadian Light Source synchrotron, using the IFS 125HR Bruker Fourier transform spectrometer. Eight of the fundamental vibrational modes of NCNCS have now been observed at high resolution. Initial analyses of the data confirm band assignments and demonstrate the accuracy of the predictions.

The empirically derived assignment of the strongly interacting 51 and 92 vibrational states of trans-HCOOH has recently been reassigned on the basis of anharmonic frequency calculations, and this, in turn, affects the assignment of many higher energy states. Here, we investigate the high-resolution synchrotron-based torsional spectrum of trans-HCOOH, and find experimental confirmation that the proposed reassignment is indeed correct, i.e., that 92 is in fact lower in energy than 51. This is largely based on examining the intensity ratio of transitions with the same rotational quantum numbers between the 92-91 and 51-91 hot bands, which indicates that the 51 [92] state has ∼31% 92 [51] character. We also examined the torsional spectrum of trans-HCOOD, and find that the intensity ratios are consistent with 92 instead being higher in energy than 61 (which is analogous to 51 in trans-HCOOD), as previously determined from higher energy spectra.

Analysis of synchrotron FTIR spectra has revealed new assignments for a number of optically pumped far-infrared laser lines from the CH 3 17 OH isotopologue of methanol, with definitive confirmation provided by recent accurate measurements of the laser frequencies. In this Note the lasing energy level systems are discussed, and the spectroscopic evidence for the assignments is presented.

The infrared Fourier transform spectrum of the OD-bending fundamental band of the CH3OD isotopologue of methanol has been investigated and analyzed in the 745–945 cm−1 region. The OD-bend is of hybrid a–b type, with predominantly parallel a-type character plus a small admixture of perpendicular b-type structure. The K-structure in the central Q-branch region is unusually well resolved and shows substantial shading to higher wavenumber. Sub-bands have been assigned for the vt = 0 ground torsional state from K = 0 to 13 for both A and E torsional species, as well as a number of sub-bands in the vt = 1, 2 excited torsional states. Upper-state term values have been determined from the observations and fitted to J(J + 1) power-series expansions to explore the torsion–K-rotation energy structure of the excited OD-bending state. A simple Fourier model for the energy structure gives a wavenumber of 863.246 cm−1 for the vt = 0 origin of the OD-bending band. The K = 0 torsional (E − A) splitting of 2.456 cm−1 found for the vt = 0 OD bend is 5.6% smaller than that of the ground state, and would correspond to a 9.9 cm−1 increase in the torsional barrier height, V3, to a value of approximately 376.2 cm−1 if other parameters do not change.

The high resolution Fourier transform spectrum of the chemically challenging sulfur dicyanide, S(CN)2, molecule was recorded at the far-infrared beamline of the synchrotron at the Canadian Light Source. The spectrum covered 50-350 cm(-1), and transitions in three fundamentals, ν4, ν7, and ν8, as well as in the hot-band sequence (n + 1)ν4 - nν4, n = 1-4, have been assigned and measured. Global analysis of over 21,300 pure rotation and rotation vibration transitions allowed determination of precise energies for 12 of the lowest vibrationally excited states of S(CN)2, including the five lowest fundamentals. These results constitute an extensive set of benchmarks for ab initio anharmonic force field calculations and the observed and calculated vibration-rotation constants and anharmonic frequencies are compared. The semiexperimental equilibrium, r(e)(SE), geometry of S(CN)2 has also been evaluated. In the course of the measurements, new information concerning the physical chemistry of S(CN)2 has been obtained.

We report on the synchrotron hard X-ray-induced decomposition of strontium oxalate (SrC2O4) pressurized to 7 GPa inside a diamond anvil cell (DAC). After some 4 h of irradiation in a white X-ray synchrotron beam, a dark reddish/brown region formed in the area of irradiation which was surrounded by a yellowish brown remainder in the rest of the sample. Upon depressurization of the sample to ambient conditions, the reacted/decomposed sample was recoverable as a dark brown/red and yellow waxy solid. Synchrotron infrared spectroscopy confirmed the strong presence of CO2 even under ambient conditions with the sample exposed to air and other strongly absorbing regions, suggesting that the sample may likely be polymerized CO (in part) with dispersed CO2 and SrO trapped within the polymer. These results will have significant implications in the ability to readily produce and trap CO2 in situ via irradiation of a simple powder for useful hard X-ray photochemistry and in the ability to easily manufacture polymeric CO (via loading of powders in a DAC or high volume press) without the need for the dangerous and complex loading of toxic CO. A novel means of X-ray-induced polymerization under extreme conditions has also been demonstrated.

An electron bunch circulating in a storage ring constitutes a dynamical system with both longitudinal and transverse degrees of freedom. Through a self-interaction with the wakefields created by the bunch, certain of these degrees may get excited, defining a set of eigenmodes analogous to a spectroscopic series. The present study focuses on the longitudinal modes of a single bunch. The excitation of a mode appears as an amplitude modulation at the mode frequency of the coherent synchrotron radiation (CSR) emitted by the bunch. The modulations are superimposed on a much larger continuum from CSR emission in the continuous mode. A given eigenmode is classified by the integer m which is the ratio of the mode frequency to the synchrotron frequency. The present measurements extend up to m=8 and focus on the region near the instability thresholds. At threshold the modes are excited sequentially, resembling a staircase when the mode frequencies are plotted as a function of bunch length or synchrotron frequency. Adjacent modes are observed to coexist at the boundaries between the modes. An energy-independent correlation is observed between the threshold current for an instability and the corresponding zero-current bunch length. Measurements were made at five beam energies between 1.0 and 2.9 GeV at the Canadian Light Source. The CSR was measured in the time domain using an unbiased Schottky diode spanning 50–75 GHz.

Far- and mid-infrared photoacoustic (PA) spectra of tetracene, pentacene, perylene and pyrene were acquired in this study. Far-infrared data were obtained at wavenumbers down to ∼80 cm −1 using large-amplitude phase modulation in a step-scan spectrometer; many previously unreported bands were observed in these spectra. For each compound, the fingerprint region of the mid-infrared spectrum (approximately 400–2000 cm −1 ) contained a large number of bands correlated with vibrations that are predicted to be either infrared or Raman active. In addition, numerous combination and overtone bands appeared in the mid-infrared spectra. This PA investigation provides the most detailed spectral data known for these four aromatic compounds.

Four vibrational levels of the five-membered ring molecule furan (C 4 H 4 O) have been rotationally analyzed from far-infrared Fourier transform spectra obtained at the Canadian Light Source synchrotron. We found that the low-lying ν 14 and ν 11 levels at 602.9 and 599.6 cm −1 interact through a second-order Coriolis resonance. This perturbation was characterized through a coupled analysis of the ν 14 and ν 18 fundamental spectra and the ν 18 – ν 11 band. The ν 19 fundamental spectrum was analyzed as well, and the data for all observed bands were combined with previously reported microwave transitions to produce the final fit. The spectra are an excellent demonstration of the high quality of data that can be obtained when far-infrared synchrotron radiation is used as the radiation source in Fourier transform spectroscopy experiments.

The Fourier transform spectrum of the CH317OH isotopologue of methanol has been recorded in the 65–1200 cm−1 spectral region at a resolution of 0.00096 cm−1 using synchrotron source radiation at the Canadian Light Source. Here we present an extension to higher torsional states of our investigation of the torsion–rotation transitions within the small-amplitude vibrational ground state, now including assignments of more than 16 500 lines involving quantum numbers in the ranges vt ⩽ 3, J ⩽ 30 and |K| ⩽ 12, as well as a study of the strong CO-stretching band centered at 1020 cm−1. Energy term values have been determined for assigned ground and CO-stretching levels by use of the Ritz program, and have been fitted to series expansions in powers of J(J + 1) to determine substate origins and effective B values. Several Fermi anharmonic and Coriolis level-crossing resonances coupling the CO stretch with high torsional ground-state levels have been identified and characterized. The study is motivated by astrophysical applications, with a principal aim being the compilation of an extensive set of energy term values to permit prediction of astronomically observable sub-millimetre transitions to within an uncertainty of a few MHz.

New astronomical facilities such as HIFI on the Herschel Space Observatory, the ALMA sub-mm telescope array and the SOFIA airborne infrared (IR) telescope will yield spectra from interstellar and protostellar sources with vastly increased sensitivity, resolution and frequency coverage. This creates the need for major enhancements to laboratory databases for the particularly abundant and widespread molecular species known as interstellar “weeds” in order to model and account for their lines in observed spectra in the search for new and more exotic interstellar molecular “flowers”. With its large-amplitude internal torsional motion, methanol has particularly rich spectra throughout the THz and far-infrared regions and, being widely distributed throughout the galaxy, is perhaps the most notorious interstellar weed. We have recorded new spectra for CH 3 OH on the high-resolution Fourier transform spectrometer on the Far-IR beamline at the Canadian Light Source synchrotron facility. New sub-band assignments for CH 3 OH are reported at high rotational and/or torsional quantum number, allowing term values for a number of new torsion–rotation substates to be determined. The aim of the program is to extend quantum number coverage of the data, improve our understanding of the energy level structure, and provide the astronomical community with better databases and models of the spectral patterns with greater predictive power for a range of astrophysical conditions.

The Fourier transform spectrum of the isotopologue of methanol has been recorded in the 120–350 cm−1 far-infrared region at a resolution of 0.00096 cm−1 using synchrotron source radiation at the Canadian Light Source. The study, motivated by astrophysical applications, is aimed at generating a sufficiently accurate set of energy level term values for the ground vibrational state to allow prediction of the centres of the quadrupole hyperfine multiplets for astronomically observable sub-millimetre transitions to within an uncertainty of a few MHz. To expedite transition identification, a new function was added to the Ritz program in which predicted spectral line positions were generated by an adjustable interpolation between the known assignments for the and isotopologues. By displaying the predictions along with the experimental spectrum on the computer monitor and adjusting the predictions to match observed features, rapid assignment of numerous sub-bands was possible. The least squares function of the Ri...

Thiophosgene (Cl2CS) is a favorite model system for studies of photophysics, vibrational dynamics, and intersystem interaction effects. But there are no previous rotationally-resolved infrared studies because the spectra are very congested due to hot bands and multiple isotopic species. This paper reports a detailed study of the ν2 (not, vert, similar504 cm−1) and ν4 (not, vert, similar471 cm−1) fundamental bands for the two most abundant isotopomers, 35Cl2CS and 35Cl37ClCS, based on spectra with observed line widths of not, vert, similar0.0008 cm−1 obtained at the Canadian Light Source far-infrared beamline using synchrotron radiation and a Bruker IFS125 Fourier transform spectrometer.

The high-resolution Fourier transform spectrum of the ν 8 CO-stretching band of CH 3 18 OH between 900 and 1100 cm −1 has been recorded at the Canadian Light Source (CLS) synchrotron facility in Saskatoon, and the majority of the torsion–rotation structure has been analyzed. For the ν t = 0 torsional ground state, subbands have been identified for K values from 0 to 11 for A and E torsional symmetries up to J values typically well over 30. For ν t = 1, A and E subbands have been assigned up to K = 7, and several ν t = 2 subbands have also been identified. Upper-state term values determined from the assigned transitions using the Ritz program have been fitted to J ( J + 1) power-series expansions to obtain substate origins and sets of state-specific parameters giving a compact representation of the substate J -dependence. The ν t = 0 subband origins have been fitted to effective molecular constants for the excited CO-stretching state and a torsional barrier of 377.49(32) cm −1 is found, representing a 0.89% increase over the ground-state value. The vibrational energy for the CO-stretch state was found to be 1007.49(7) cm −1 . A number of subband-wide and J -localized perturbations have been seen in the spectrum, arising both from anharmonic and Coriolis interactions, and several of the interacting states have been identified.

We report on high resolution measurements of resonances in the spectrum of coherent synchrotron radiation (CSR) at the Canadian Light Source (CLS). The resonances permeate the spectrum at wavenumber intervals of $0.074 ~\textrm{cm}^{-1}$, and are highly stable under changes in the machine setup (energy, bucket filling pattern, CSR in bursting or continuous mode). Analogous resonances were predicted long ago in an idealized theory as eigenmodes of a smooth toroidal vacuum chamber driven by a bunched beam moving on a circular orbit. A corollary of peaks in the spectrum is the presence of pulses in the wakefield of the bunch at well defined spatial intervals. Through experiments and further calculations we elucidate the resonance and wakefield mechanisms in the CLS vacuum chamber, which has a fluted form much different from a smooth torus. The wakefield is observed directly in the 30-110 GHz range by RF diodes, and indirectly by an interferometer in the THz range. The wake pulse sequence found by diodes is less regular than in the toroidal model, and depends on the point of observation, but is accounted for in a simulation of fields in the fluted chamber. Attention is paid to polarization of the observed fields, and possible coherence of fields produced in adjacent bending magnets. Low frequency wakefield production appears to be mainly local in a single bend, but multi-bend effects cannot be excluded entirely, and could play a role in high frequency resonances. New simulation techniques have been developed, which should be invaluable in further work., 5 figures. Differs from first posting by correction of typo and inclusion of responses to referee's questions

Author Institution: Canadian Light Source Inc. 101 Perimeter Road, Saskatoon SK; S7N 0X4, Canada

We report the first high-resolution measurement of superradiance, using coherent synchrotron radiation in the terahertz region from the Canadian Light Source synchrotron and a Michelson interferometer with a nominal frequency resolution of $0.000\text{ }96\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$. Superradiance arises when a high degree of phase coherence exists between the radiation fields of the individual electron bunches, and manifests itself as a series of narrow spectral peaks at harmonics of the bunch frequency. We observe an enhancement factor of 16 at the spectral peaks, limited by the interferometer resolution. The spectral distribution and relative amplitudes of the superradiant peaks are modified by altering the pattern of bunches along the bunch train.

In this work, terahertz and Fourier transform far-infrared (FTFIR) synchrotron spectra of methyl mercaptan, CH(3)SH, have been investigated in order to provide new laboratory information for enhanced observations of this species in interstellar molecular clouds and star-forming regions. Like its methanol cousin, methyl mercaptan has particularly rich spectra associated with its large-amplitude internal rotation that extend throughout the THz and FIR regions. We have recorded new spectra for CH(3)SH from 1.1-1.5 and 1.790-1.808 THz at the University of Cologne as well as high-resolution FTFIR synchrotron spectra from 50-550 cm(-1) at 0.001 cm(-1) resolution on the far-IR beam-line at the Canadian Light Source. Assignments are reported for rotational quantum numbers up to J ≈ 40 and K ≈ 15, and torsional states up to v(t) = 2 for the THz measurements and v(t) = 3 for the FTFIR observations. The THz and FTFIR measurements together with literature results have been combined in a global analysis of a dataset comprising a total of 1725 microwave and THz frequencies together with ~18000 FTFIR transitions, ranging up to v(t) = 2 and J(max) = 30 for MW∕THz and 40 for FTFIR. The global fit employs 78 torsion-rotation parameters and has achieved a weighted standard deviation of ~1.1. A prediction list (v(t) ≤ 2, J ≤ 45 and K ≤ 20) has been generated from the model giving essentially complete coverage of observable CH(3)(32)SH transitions within the bandwidths of major new astronomical facilities such as HIFI (Heterodyne Instrument for the Far Infrared) on the Herschel Space Observatory, ALMA (Atacama Large Millimeter Array), SOFIA (Stratospheric Observatory For Infrared Astronomy) and APEX (Atacama Pathfinder Experiment) to close to spectroscopic accuracy.

We produced coherent synchrotron radiation at the Canadian Light Source between about 5 and 30 cm(-1) in bursting and continuous emission modes and used it to acquire photoacoustic spectra of solids. A band was observed in the spectrum of α-lactose monohydrate at 18 cm(-1) and attributed to a rotational mode, in agreement with published data obtained using other numerical and experimental techniques.

We present a detailed spectroscopic study of carbon dioxide in support of atmospheric remote sensing. We have studied two weak absorption bands near the strong ν2 band that is used to derive atmospheric temperature profiles. We have analyzed our laboratory spectra recorded with the synchrotron and globar sources with spectral line profiles that reproduce the absorption features with high accuracy. The Q‐branch transitions exhibited asymmetric line shape due to weak line‐mixing. For these weak transitions, we have retrieved accurate experimental line strengths, self‐ and air‐broadening, self‐ and air‐induced shift coefficients and weak line mixing parameters. The experimental precision is sufficient to reveal inherent variations of the width and shift coefficients according to transition quantum numbers.

Coherent synchrotron radiation (CSR) is now an established source of radiation in the terahertz region, with flux capabilities many orders of magnitude higher than conventional SR sources. Accordingly, CSR is playing an ever-increasing role in the field of Far-IR spectroscopy at synchrotron facilities around the world. However, with the improvement in spectroscopic resolution, the incident CSR spectra from several facilities are displaying intensity profiles that appear to be modulated by periodic peaks or deep indentations, while theory predicts a featureless distribution. After eliminating the usual suspects, like multiple reflections from windows, etc., one looks for a deeper explanation, such as the role played by the radiation impedance. This impedance is largely defined by the vacuum chamber in the region of the bend magnets, but probably with some effects from the straight sections as well.

The C-N stretching infrared fundamental of CH(3)NH(2) has been investigated by high-resolution laser sideband and Fourier transform synchrotron spectroscopy to explore the energy level structure and to look for possible interactions with high-lying torsional levels of the ground state and other vibrational modes. The spectrum is complicated by two coupled large-amplitude motions in the molecule, the CH(3) torsion and the NH(2) inversion, which lead to rich spectral structure with a wide range of energy level splittings and relative line intensities. Numerous sub-bands have been assigned for K values ranging up to 12 for the stronger a inversion species for the v(t) = 0 torsional state, along with many of the weaker sub-bands of the s species. The C-N stretching sub-state origins have been determined by fitting the upper-state term values to J(J + 1) power-series expansions. For comparison with the ground-state behaviour, both ground and C-N stretch origins have been fitted to a phenomenological Fourier series model that produces an interesting pattern with the differing periodicities of the torsional and inversion energies. The amplitude of the torsional energy oscillation increases substantially for the C-N stretch, while the amplitude of the inversion energy oscillation is relatively unchanged. Independent inertial scale factors ρ were fitted for the torsion and the inversion and differ significantly in the upper state. The C-N stretching vibrational energy is determined to be 1044.817 cm(-1), while the effective upper state B-value is 0.7318 cm(-1). Several anharmonic resonances with v(t) = 4 ground-state levels have been observed and partially characterized. A variety of J-localized level-crossing resonances have also been seen, five of which display forbidden transitions arising from intensity borrowing that allow determination of the interaction coupling constants.