Far-infrared Beamline Research Articles

Mono- and di-deuterated ammonias: Far-infrared spectra and spectroscopic parameters in the ground state

Transitions of NH2D and ND2H have been detected in the high resolution spectrum of 14ND3 recorded at unapodized resolution of 0.00096 cm−1 in the region 60–600 cm−1 using the Bruker IFS 125 Fourier transform spectrometer located at the synchrotron far-infrared beamline, Canadian Light Source. In this study we report on the observation and analysis of the spectrum for the ground state of NH2D and ND2H. 2153 rotation and rotation-inversion transitions, with J up to 24, were assigned for NH2D, and 3214 transitions, with J up to 28, for ND2H. The newly assigned transitions, together with those present in the literature, were fitted on the basis of a Watson-type S reduced Hamiltonian using the IIIr and IIIl representations for NH2D and ND2H, respectively. The model Hamiltonian includes terms up to the 10th power of the angular momentum and vibration–rotation interaction terms between the inversion states. Precise and extended sets of spectroscopic effective parameters were derived for both isotopologues as results of least squares weighted fit procedures that reproduce the transition wavenumbers at experimental accuracy.

Far-infrared synchrotron-based spectroscopy of CH3SH from 50 to 560 cm−1: Near-free-rotor torsion-rotation structure and torsion-vibration interactions

Analysis of torsion-rotation structure in the far-infrared Fourier transform synchrotron spectrum of CH332SH recorded from 50 to 560 cm−1 at the Far-Infrared Beamline of the Canadian Light Source has been extended to higher near-free rotor torsional states reaching up into the region of the small-amplitude vibrations. A variety of sub-bands has been assigned for torsional quantum number up to vt = 5, expanding the database of ground-state energy term values to higher K and vt levels to provide a broad foundation for associated investigations of the vibrational spectrum. The origins of the high-vt sub-states fit quite well to a pattern of free-rotor parabolic curves as a function of K, but with a lower value of the torsional constant F than obtained from previous global analysis of lower-vt data. Numerous resonances perturbing and mixing coupled near-degenerate sub-states have been observed, arising from interactions both within the ground state and between ground and excited vibrational levels.

FTIR synchrotron spectroscopy of the S–H stretching fundamental of the 12CH332SH species of methyl mercaptan

ABSTRACTThe infrared Fourier transform spectrum of the S–H stretching fundamental band of 12CH332SH has been recorded using synchrotron radiation at the far-infrared beamline of the Canadian Light Source in Saskatoon. The S–H stretch is a hybrid band predominantly of perpendicular b-type with a small parallel a-component. With both ΔK = +1 and ΔK = −1 sub-bands present, the assignments are well determined from ground-state combination difference relations. The identified sub-bands access S–H stretching ground torsional substates from K′ = 0–14 for A and E torsional species. The substate origins have been obtained by expanding the term values in J(J + 1) power series, and have been fitted to a simple 6-parameter Fourier Hamiltonian to deduce the torsional energies. The oscillation amplitude of the S–H stretching torsional curves is 0.547 cm−1 compared to 0.653 cm−1 for the ground state, implying an increase on the order of 6.9% in the torsional barrier height. The vibrational wavenumber for the S–H stretch mode is found to be 2603.5 cm−1.

Infrared absorption cross sections of propane broadened by hydrogen

Fourier transform infrared absorption cross-sections of pure propane (C3H8) and propane broadened with H2 have been calculated from transmittance spectra recorded at temperatures from 292K to 205K. Transmittance spectra were recorded at the Canadian Light Source (CLS) Far-Infrared beamline, utilizing both the synchrotron source and the internal glowbar source. The absorption cross-sections have been calibrated to Pacific Northwest National Laboratory (PNNL) reference cross-sections of propane and can be used to interpret astronomical observations of giant planets such as Jupiter and Saturn as well as exoplanets.

The high resolution spectrum of 15NH3 in the far-infrared: Rotation-inversion transitions in the ground, v2=1, 2 and v4=1 states

The high resolution spectrum of 15NH3 has been recorded at unapodized resolution of 0.00096cm−1 in the region 60–600cm−1 using the Bruker IFS 125 Fourier transform spectrometer located at the far-infrared beam-line, Canadian Light Source. We report on the observation and analysis of the rotation-inversion spectrum in the ground, v2=1, 2 and v4=1 states. All the rotation-inversion transitions in the ground state together with the pure inversion transitions present in the literature were fitted simultaneously on the basis of a rotation-inversion Hamiltonian which includes distortion constants up to the 12th power in the angular momentum and the Δk=±3 and Δk=±6 interaction terms. A set of effective parameters was also obtained for the v2=1 state adopting the same theoretical model. For the v2=2 and v4=1 states only a list of observed transitions is reported. The wavenumbers of all the assigned transitions were compared with their theoretically predicted values [S.N. Yurchenko, J. Quant. Spectrosc. Radiat. Transf., 2015, 152, 28]. The present results noticeably improve the wavenumber line list in the HITRAN data base [L. S. Rothman et al. J. Quant. Spectrosc. Radiat. Transf.,2013, 130, 4].

Improved rovibrational constants for the v7 = 1 state of ethylene-cis-1,2-d2 (cis-C2H2D2) by high-resolution synchrotron FTIR spectroscopy

Using the far-infrared beamline of the Australian Synchrotron, the spectrum of the ν7 band of ethylene-cis-1,2-d2 (cis-C2H2D2) was recorded in the 640–990cm−1 region at an unapodized resolution of 0.00096cm−1. A rovibrational analysis of a total of 2823 infrared transitions of the ν7 band was carried out using an asymmetric rotor fitting program based on the Watson’s A-reduced Hamiltonian in the Ir representation to derive up to four sextic constants with a rms deviation of 0.00035cm−1. From the fitting of 2634 ground state combination differences (GSCDs) of cis-C2H2D2 which were derived from the infrared transitions of the ν7 band of this work, and ν10 and ν12 bands of previous studies, together with 22 microwave frequencies, accurate ground state constants of cis-C2H2D2 up to four sextic terms were obtained. The rotational constants (A, B, and C) of the v7=1 state of cis-C2H2D2 were found to agree within 0.5% with the calculated values using B3LYP/cc-pVTZ and MP2/cc-pVTZ levels of theory. From this work, the band center of ν7 at 842.209489(20)cm−1 and the rovibrational constants of the v7=1 state of cis-C2H2D2 were determined with better accuracy than previously reported.

High-resolution Fourier transform synchrotron spectroscopy of the C–S stretching band of methyl mercaptan, CH332SH

The C–S stretching fundamental band of 12CH332SH, the principal isotopologue of methyl mercaptan, has been investigated by Fourier transform infrared spectroscopy on the Far-Infrared beamline at the Canadian Light Source synchrotron. The band is centered around 710cm−1 and shows well-resolved a-type parallel structure. Most of the A and E spectral sub-bands have been assigned up to K=12 for the vt=0 torsional state and K=9 for the vt=1 state, along with a smaller variety of sub-bands for vt=2. C–S stretching energy term values have been determined employing known ground-state energies, and have been fitted to series expansions in powers of J(J+1) to determine the substate origins. The origins have in turn been fitted to a Fourier model to characterize the oscillatory torsional energy structure of the C–S stretching state. The amplitude of oscillation of the vt=0 torsional curves is significantly larger for the C–S stretch state compared to the ground state. A strategy devised to relate this amplitude to an effective torsional barrier height indicates a decrease of about 7% in the effective V3 for the C–S stretch. The vibrational frequency determined for the stretching fundamental from the Fourier fit is 710.3cm−1. The C–S stretching manifold is crossed by excited vt=4 torsional levels of the ground state, and strong torsion–vibrational resonant coupling is observed via perturbations in the spectrum together with forbidden sub-bands induced by mixing and intensity borrowing.

Synchrotron infrared spectroscopy of the ν4, ν8, ν10, ν11 and ν14 fundamental bands of thiirane

The high-resolution spectrum of thiirane has been recorded using the far-infrared beamline at the Australian synchrotron facility. Spectra have been recorded between 700cm−1 and 1200cm−1 and ro-vibrational transitions associated with four fundamental bands of thiirane have been observed and assigned. The effects of Coriolis coupling were observed in the upper energy levels associated with the ν4 (1024cm−1) and the ν14 (1050cm−1) fundamental bands as well as in the ν11 (825cm−1) and the ν8 (895cm−1) fundamental bands. The ν10 (945cm−1) fundamental band was also observed and was found to have no significant perturbations associated with it. For each of the observed bands rotational and centrifugal distortion constants have been evaluated, while for all but the ν10 fundamental band, Coriolis interaction parameters have been determined for the upper states. The ground state constants have also been further refined.

High-resolution synchrotron infrared spectroscopy of thiophosgene: The ν1, ν5, 2ν4, and ν2 + 2ν6 bands

Thiophosgene (Cl2CS) is a favorite model system for studies of photophysics, vibrational dynamics, and intersystem interactions. But its infrared spectra tend to be very congested due to hot bands and multiple isotopic species. This paper reports the first detailed study of the ν1 (∼1139cm−1) and ν5 (∼820cm−1) fundamental bands for the two most abundant isotopologues, 35Cl2CS and 35Cl37ClCS, based on spectra with a resolution of about 0.001cm−1 obtained at the Canadian Light Source far-infrared beamline using synchrotron radiation and a Bruker IFS125 Fourier transform spectrometer. The 2ν4 (∼942cm−1) and ν2+2ν6 (∼1104cm−1) bands are also studied here, but the ν2+ν6 band (∼795cm−1) resisted full analysis.

High-resolution Fourier transform infrared synchrotron spectroscopy of the NO2 in-plane rock band of nitromethane

The high-resolution rotationally resolved Fourier-transform infrared spectrum of the NO2 in-plane rock band (440–510cm−1) of nitromethane (CH3NO2) has been recorded using the Far-Infrared Beamline at the Canadian Light Source, with a resolution of 0.00096cm−1. About 1773 transitions reaching the upper state levels m′=0;Ka′⩽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 limits of rovibrational analysis: the severely entangled ν1 Polyad vibration of dichlorodifluoromethane in the greenhouse IR window.

Five intense bands of dichlorodifluoromethane (CFC-12, or R12) in the infrared atmospheric window help make it a major greenhouse contributor. These include the ν1 fundamental at 1101.4 cm(-1) and the ν2 + ν3 combination at 1128.6 cm(-1). High-resolution spectra measured using the Australian Synchrotron Far-Infrared beamline were analyzed, and transitions of C(35)Cl2F2 were assigned to ν1, ν2 + ν3, and the ν3 + 2ν5 combination at 1099.7 cm(-1). The (v3 = 1; v5 = 2) state couples indirectly to v1 = 1 via Fermi resonances linking both states with v2 = v3 = 1. The v1 = 1 rotational levels are further riddled with perturbations and avoided crossings due to Coriolis resonance with the upper vibrational states of ν2+ ν9 at 1102.4 cm(-1) and (indirectly) ν2 + ν7 at 1105.8 cm(-1). A global treatment of all these states fits the observed line positions and satisfactorily accounts for the significant intensity of ν2 + ν3. Spectral simulations elucidate resonance perturbations that affect the distribution of IR absorption in the CF stretch region, and consequently the global warming potential of R12. Combination levels derived from rovibrational analysis lead to reassessment of the gas phase wavenumber values for the ν3 (458.6 cm(-1)), ν7 (437.7 cm(-1)) and ν9 (436.9 cm(-1)) fundamentals of C(35)Cl2F2, consistent with a cold, vapor phase far IR spectrum and previously published solid state spectra. B3LYP and MP2 anharmonic frequency calculations provide further support. At the MP2/aug-cc-pVTZ level, the root mean square (r.m.s.) error for unscaled anharmonic fundamentals is 6.2 cm(-1), decreased to 1.7 cm(-1) if only considering the seven lowest wavenumber modes, and integrated band intensities according with experimental literature values. Smaller basis sets produce band strengths that are too high. Low-resolution band assignments are reported for C(35)Cl(37)ClF2, C(37)Cl2F2, and (13)C(35)Cl2F2.

Line shape study of the carbon dioxide laser band Ι

The spectral line parameters of carbon dioxide have been measured in the laser band I (00011 ← 10001) centred at 10.4 μm. The spectra were recorded at room temperature using the spectroscopic instrumentation at the far-infrared beamline, Canadian Light Source, Saskatoon, Sask. The spectral line intensities, air- and self- broadened Lorentz half widths, and pressure-induced shift coefficients were retrieved for 48 spectral lines using a multispectrum fit technique (Benner et al. J. Quant. Spectrosc. Radiat. Transfer, 53, 705 (1995)). Line parameters were retrieved using the Voigt and speed-dependent Voigt models. The deviations between our results and other results reported in the literature and in the HITRAN08 (Rothman et al. J. Quant. Spectrosc. Radiat. Transfer, 110, 533 (2009)) database were examined and discussed. The effect of errors in fitting channel spectra parameters was examined and found to be mitigated by the inclusion of channels in the multispectral fit.

Far-Infrared Spectrum of S(CN)2 Measured with Synchrotron Radiation: Global Analysis of the Available High-Resolution Spectroscopic Data

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.

Synchrotron far infrared spectroscopy of the ground, ν5, and ν15 states of thiirane

The high-resolution (0.001 cm(-1)) spectrum of thiirane has been recorded at the far-infrared beamline at the Australian synchrotron between 760-400 cm(-1) and 170-10 cm(-1). Ro-vibrational transitions of the highly Coriolis coupled ν(5) (628.1 cm(-1)) and ν(15) (669.7 cm(-1)) fundamentals, as well as pure rotational far-IR transitions have been assigned, and rotational, centrifugal distortion, and Coriolis interaction parameters determined. ν(15) gains the vast majority of its intensity from an interesting Coriolis intensity stealing mechanism, which is also outlined.

High-resolution FTIR spectroscopy of the ν7 and ν8 bands of 1-phosphapropyne

1-Phosphapropyne has been prepared and high-resolution (0.001cm−1) spectra have been recorded on the far-infrared beamline at the Australian synchrotron between 1500–700cm−1 and 400–50cm−1. Ro-vibrational transitions of the ν8 (308cm−1) and ν7 (1006cm−1) fundamentals as well as the 2ν8±2←v8±1 and 2ν80←v8±1 hot-bands have been assigned, and rotational, centrifugal distortion and Coriolis interaction parameters determined. The 2ν8±2←v8±1 hot-band is an example of a particularly complex E←E transition, for which both states are strongly Coriolis and l(2,2) coupled.

The far infrared spectrum of trans-formic acid: An extension up to 175 cm−1

The far infrared spectrum of HCOOH was recorded at a high resolution (0.0009cm−1) and long path length (72m) at the far-infrared beamline, Canadian Light Source. Spectra were recorded in the region 62–300cm−1, showing transitions from the trans-isomer.Ground state rotational transitions with Ka up to 30, were identified up to 175cm−1, extending the observation reported in the literature. A total of 3321 transitions were assigned and fitted together with previous (4149) published data. An improved set of rotational parameters was obtained adopting the symmetric top (A) reduction of the rotational Hamiltonian in the Ir representation. The newly measured far infrared transitions allowed the determination of all diagonal and off diagonal 8th order parameters L and of some of the diagonal 10th order parameters P.

The far-infrared spectrum of 12C2HD

The infrared spectrum of 12C2HD has been studied using synchrotron radiation at the far-infrared beam line, Canadian Light Source, Saskatoon, Canada. The spectra were recorded at a resolution of 0.00096 cm−1 in the 60 to 360 cm−1 range using a Bruker IFS 125 Fourier transform spectrometer. In total, 821 vibration rotation lines were observed and assigned to the P(J), Q(J) and R(J) transitions of the ν 5 ← ν 4 difference band and associated hot bands with J″ up to 35 and (ν 4 + ν 5) up to 3. These new transitions were analysed together with 4518 transitions involving bending states with (ν 4 + ν 5) up to 3 available in the literature. The spectroscopic parameters obtained from the fit reproduce 4909 transitions with a standard deviation of 0.00028 cm−1. The ν 5 ← ν 4 bands of 13CH12CD and 12CH13CD were also detected and analysed.

The high resolution infrared spectrum of the v 4 band of 1,1,1-trifluoroethane

The v 4 band of 1,1,1-trifluoroethane (CH3CF3) has been studied using synchrotron radiation at the far-infrared beamline, Canadian Light Source. The spectra were recorded at a resolution of 0.00096 cm−1 in the spectral range 800 to 860 cm−1 using a Bruker IFS125 FT spectrometer. Altogether 2785 lines were assigned to qPK (J) and qRK (J) transitions with J ″ up to 71 and K up to 45. The qQK (J) sub-branches are too congested and overlapped to other hot-band Q branches to be analysed. A Watson-type Hamiltonian containing the usual terms up to the 6th power in the angular momentum operators was used in the analysis. The spectroscopic parameters obtained from the fit reproduce 2636 transitions with a standard deviation of about 0.00016 cm−1.

High-resolution synchrotron infrared spectroscopy of thiophosgene: The ν2 and ν4 fundamental bands near 500 cm −1

Thiophosgene (Cl 2CS) 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 ν 2 (∼504 cm −1) and ν 4 (∼471 cm −1) fundamental bands for the two most abundant isotopomers, 35Cl 2CS and 35Cl 37ClCS, based on spectra with observed line widths of ∼0.0008 cm −1 obtained at the Canadian Light Source far-infrared beamline using synchrotron radiation and a Bruker IFS125 Fourier transform spectrometer.

Performance of the far-IR beamline of the 6 MeV tabletop synchrotron light source

The performance of the far-infrared (FIR) beamline of the 6 MeV tabletop synchrotron light source MIRRORCLE-6FIR dedicated to far-infrared spectroscopy is presented. MIRRORCLE-6FIR is equipped with a perfectly circular optical system (PhSR) placed around the 1 m-long circumference electron orbit. To illustrate the facility of this light source, the FIR output as well as its spectra were measured. The optimum optical system was designed by using the ray-tracing simulation code ZEMAX. The measured FIR intensity with the PhSR in place is about five times higher than that without the PhSR, which is in good agreement with the simulation results. The MIRRORCLE-6FIR spectral flux is compared with a standard thermal source and is found to be 1000 times greater than that from a typical thermal source at approximately 15 cm(-1). It is also observed that the MIRRORCLE-6FIR radiation has a highly coherent nature. The broadband infrared allows the facility to reach the spectral range from 10 cm(-1) to 100 cm(-1). MIRRORCLE-6FIR, owing to a large beam current, the PhSR mirror system, a large dynamic aperture and small ring energy, can deliver a bright flux of photons in the FIR/THz region useful for broadband spectroscopy.