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Abstract: Lorentz pressure-broadening and pressure-induced shift coefficients along with their temperature dependences have been determined for over forty P- and R-branch transitions in the fundamental band of 12C16O broadened with helium. A total of nineteen spectra recorded at various temperatures (+24 to −194°C) in the 2010–2260cm−1 spectral region were analyzed simultaneously using a multispectrum nonlinear least squares fitting technique. The spectra were recorded with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak. Present results are compared with similar measurements reported recently. [Copyright &y& Elsevier]

Highlights • 5819 line positions and intensities were retrieved from measured spectra in the 5550- 5825 cm−1 region. • More than 2800 new assignments were made in the region. • More than 3445 experimental line positions were modeled to 0.0024 cm−1. Abstract A new study of 12CH 4 line positions and intensities was performed for the Tetradecad regions 5550,000–5695.250, 5718.8–5724.250 and 5792.36–5814.290 cm−1 using long path (202 m, 602 m, 1604 m and 1804 m) spectra of normal samples of CH 4 at different pressures recorded with a Fourier transform spectrometer in Reims, France. Line positions and intensities were retrieved by least squares curve-fitting procedures and analyzed using the effective Hamiltonian and the effective dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. An 80 K spectrum recorded in Jet Propulsion Laboratory (JPL), Pasadena, of enriched 12CH 4 was used for low-J line positions. Another 80 K spectrum of enriched 13CH 4 from JPL was used to discern the isotopic lines. A new measured linelist contains positions and intensities for 5819 features. Quantum assignments were made for more than 3400 transitions, which represent ∼95% of the integrated line intensity observed in this region. All assigned 3445 line positions were fitted with RMS standard deviations of 0.0024 cm−1. The sum of observed intensities between 5550 and 5695 cm−1 fell within 2% of the predicted value from ab initio variational calculations reported in the TheoReTS database (http://theorets.univ-reims.fr ; http://theorets.tsu.ru). [ABSTRACT FROM AUTHOR]

A new study of 12 CH 4 line positions and intensities was performed for part of the Tetradecad region between 5300 and 5550 cm −1 using four long path (202 m, 602 m, 1604 m and 1804 m) spectra of normal samples of CH 4 at different pressures recorded with a Fourier transform spectrometer in Reims, France. Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. An 80 K spectrum from JPL of enriched 12 CH 4 was used for low-J line positions. One other 80 K spectrum from JPL of enriched 13 CH 4 was used to discern the isotopic lines. A new measured linelist contains positions and intensities for 5934 features. Quantum assignments were made for 2847 transitions, which represent ∼90% of the integrated line intensity observed in this region. All assigned line positions and 2227 selected line intensities were fitted with RMS standard deviations of 0.0025 cm −1 and 8.6%, respectively. The sum of observed intensities between 5300 and 5550 cm −1 fell within 2% of the predicted value from ab initio variational calculations. [ABSTRACT FROM AUTHOR]

We report revisited experimentally retrieved and theoretically calculated He-broadened Lorentz half-width coefficients and He- pressure-shift coefficients of 45 carbon monoxide transitions in the 1←0 band. The spectra analyzed in this study were recorded over a range of temperatures between 79 and 296 K. The He-broadened line parameters and their temperature dependences were retrieved using a multispectrum nonlinear least squares analysis program. The line shape models used in this study include Voigt, speed dependent Voigt, Rautian (to take into account confinement narrowing) and Rautian with speed dependence, all with an asymmetric component added to account for weak line mixing effects. We were unable to retrieve the temperature dependence of line mixing coefficients. A classical method was used to determine the He-narrowing parameters while quantum dynamical calculations were performed to determine He-broadening and He-pressure shifts coefficients at different temperatures. The line mixing coefficients were also derived from the exponential power gap law and the energy corrected sudden approximation. The current measurements and theoretical results are compared with other published results, where appropriate. [ABSTRACT FROM AUTHOR]

This paper presents the results of a spectroscopic line shape study of self- and nitrogen-broadened 12 CH 3 D transitions in the ν 3 and ν 5 bands in the Triad region. We combined five pure gas spectra with eighteen spectra of lean mixtures of 12 CH 3 D and nitrogen, all recorded with a Bruker IFS-125 HR Fourier transform spectrometer. The spectra have been analyzed simultaneously using a multispectrum nonlinear least squares fitting technique. N 2 -broadened line parameters for 184 transitions in the ν 3 band and 205 transitions in the ν 5 band were measured. In addition, line positions and line intensities were measured for 168 transitions in the ν 3 band and 214 transitions in the ν 5 band. We have observed 10 instances of weak line mixing corresponding to K ″=3 A1 or A2 transitions. Comparisons were made for the N 2 -broadening coefficients and associated temperature exponents with corresponding values calculated using a semi-classical Robert Bonamy type formalism that involved an inter-molecular potential with terms corresponding to short- and long-range interactions, and exact classical molecular trajectories. The theoretical N 2 -broadened coefficients are overestimated for high J values, but are in good agreement with the experimental values for small and middle range J values. [ABSTRACT FROM AUTHOR]

A new study of 13 CH 4 line intensities and positions was performed in the Octad region between 3750 and 4700 cm −1 . Using 13 C-enriched samples, spectra were recorded with both the McMath–Pierce FTS at Kitt Peak Observatory in Arizona and the Bruker IFS-125HR at JPL. Sample temperatures ranged between 80 and 296 K. Line positions and intensities of ~15,000 features were retrieved at different temperatures by non-linear least squares curve-fitting procedures. Intensities were used to estimate the lower state energies for 60% of the features in order to determine quantum assignments up to J =10. A preliminary analysis was performed using the effective Hamiltonian and the effective dipole transition moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. Selected assignments were made up to J =10 for all 24 sub-vibrational states of the Octad; these were modeled for 4752 experimental line positions and 3301 selected line intensities fitted with RMS standard deviations of 0.004 cm −1 and 6.9%, respectively. Integrated intensities of the eight Octad bands are compared to ab initio variational calculations. A prediction of the 13 CH 4 is given, but further analysis to improve the calculation will be reported in the future. [ABSTRACT FROM AUTHOR]

The temperature-dependences of line broadening and shift parameters for many 12 CH 3 D transitions have been determined using six high-resolution, high signal-to-noise ratio, room-temperature CH 3 D (98% purity) and CH 3 D-N 2 spectra recorded with 25 cm path length ( at 0.01 cm −1 unapodized resolution) using the McMath−Pierce FTS located on Kitt Peak, Arizona, and 17 additional high quality, pure CH 3 D (99% purity) and CH 3 D-N 2 spectra recorded between 79 and 296 K with the 20.38 cm path coolable cell (at 0.0056 cm −1 unapodized resolution) with the Bruker 125HR FTS at the Jet Propulsion Laboratory (JPL), Pasadena, California. The spectra have been fitted simultaneously applying a multispectrum nonlinear least-squares technique. In the analysis, the Lorentzian N 2 -broadened half-width coefficients and the corresponding pressure-shift coefficients as well as their temperature dependences are extracted for about 400 transitions (0≤ J ″≤19, K ″≤16) in the perpendicular (Δ K =±1) ν 6 band. At 296 K, the measured N 2 -broadened half-width coefficients range from 0.0209 to 0.0782 cm −1 atm −1 whereas the majority of the associated N 2 -induced shift coefficients are negative, and the values are between -0.016 and 0.005 cm −1 atm −1 . The temperature dependence exponents for N 2 -broadened half-widths range between 0.264 and 0.924, whereas the temperature dependence coefficients for N 2 -induced shifts are between 0 and 0.00011 cm −1 atm −1 K −1 . The N 2 -broadened half-width coefficients have been also calculated using a semi-classical approach based on a rigorous treatment of the active molecule as a symmetric top, a model intermolecular potential comprising both short- and long-range interactions, and exact classical trajectories. The role of the various high-order multipoles in the line-broadening at low, middle and high values of the rotational quantum number J ″ has been investigated and the main features of the K -dependences analyzed. The calculations performed for 296, 240 and 190 K have allowed to deduce the half-width temperature-dependence exponents, completing the general comparison of our new experimental results with those which are available in the literature. [ABSTRACT FROM AUTHOR]

Abstract: A new study of 12CH3D line positions and intensities was performed for the upper portion of the Enneadecad polyad between 4000 and 4550cm−1. For this, FTIR spectra were recorded with D-enriched methane samples (at 80K with a Bruker 125 IFS at 0.005cm−1 resolution and at 291K with the McMath-Pierce FTS at 0.011cm−1 resolution, respectively). Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective dipole moment expressed in terms of irreducible tensor operators adapted to symmetric top molecules. Initially, only the cold spectrum was used to identify quantum assignments and predict 12CH3D relative intensities in this region. To assign higher quanta up to J equal 14, additional line positions and intensities were obtained from two room temperature spectra. In the final stage, measured intensities from both the cold and the room temperature data were normalized to corresponding values at 296K and then averaged. Combining the two temperature datasets confirmed the assumed quantum assignments and also demonstrated the relative accuracies to be better than ±0.0002cm−1 for line positions and at least ±6% for intensities so that ∼1160 features were selected. Including additional assignments from the room temperature spectra alone permitted 1362 line intensities of 11 bands (involving 23 vibrational symmetry components) to be reproduced with an RMS of 9%. Over 4085 selected positions for 12 bands were modeled to 0.008cm−1. Nevertheless a number of known assignments could not be modeled to within our experimental precisions. More work is needed to obtain a complete characterization of this complex polyad. [Copyright &y& Elsevier]

Abstract: Temperature dependences of pressure-broadened half-width and pressure-induced shift coefficients along with accurate positions and intensities have been determined for transitions in the 2←0 band of 12C16O from analyzing high-resolution and high signal-to-noise spectra recorded with two different Fourier transform spectrometers. A total of 28 spectra, 16 self-broadened and 12 air-broadened, recorded using high-purity (≥99.5% 12C-enriched) CO samples and CO diluted with dry air (research grade) at different temperatures and pressures, were analyzed simultaneously to maximize the accuracy of the retrieved parameters. The sample temperatures ranged from 150 to 298K and the total pressures varied between 5 and 700Torr. A multispectrum nonlinear least squares spectrum fitting technique was used to adjust the rovibrational constants (G, B, D, etc.) and intensity parameters (including Herman–Wallis coefficients), rather than determining individual line positions and intensities. Self- and air-broadened Lorentz half-width coefficients, their temperature dependence exponents, self- and air-pressure-induced shift coefficients, their temperature dependences, self- and air- line mixing coefficients, their temperature dependences and speed dependence have been retrieved from the analysis. Speed-dependent line shapes with line mixing employing off-diagonal relaxation matrix element formalism were needed to minimize the fit residuals. This study presents a precise and complete set of spectral line parameters that consistently reproduce the spectrum of carbon monoxide over terrestrial atmospheric conditions. [Copyright &y& Elsevier]

Abstract: Ethane is a prominent contributor to the spectrum of Titan, particularly in the ν9 region centered near 822cm−1. To improve the spectroscopic line parameters at 12μm, 41 high-resolution (0.0016–0.005cm−1) absorption spectra of C2H6 were obtained at sample temperatures between 211 and 298K with the Bruker IFS 120HR at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington. Two additional spectra were later recorded at ∼150K using a new temperature-stabilized cryogenic cell designed for the sample compartment of the Bruker IFS 125HR at the Jet Propulsion Laboratory (JPL) in Pasadena, California. A multispectrum nonlinear least-squares fitting program was applied simultaneously to all 43 spectra to measure the line positions, intensities, N2- and self-broadened half-width coefficients and their temperature dependences. Reliable pressure-induced shift coefficients could not be obtained, however, because of the high congestion of spectral lines (due to torsional-split components, hot-band transitions as well as blends). Existing theoretical modeling of this very complicated ν9 region permitted effective control of the multispectrum fitting technique; some constraints were applied using predicted intensity ratios, doublet separations, half-width coefficients and their temperature dependence exponents in order to determine reliable parameters for each of the two torsional-split components. For 12C2H6, the resulting retrievals included 17 pQ and rQ sub-bands of ν9 (as well as some pP, rR sub-bands). Positions and intensities were measured for 3771 transitions, and a puzzling difference between previously measured ν9 intensities was clarified. In addition, line positions and intensities were obtained for two 12C2H6 hot bands (ν9+ν4−ν4, ν9+2ν4−2ν4) and the ν9 band of 13C12CH6, as well as several hundred presently unidentified transitions. N2- and self-broadened half-width coefficients were determined for over 1700 transitions, along with 1350 corresponding temperature dependence exponents. Similar to N2- and self-broadened half-width coefficients, their temperature dependence exponents were also found to follow distinctively different patterns. However, while the self- and N2-broaded widths differed by 40%, the temperature dependence exponents of the two broadening gases were similar. The variations of the observed half-width coefficients and their temperature dependences with respect to J, K quantum numbers were modeled with a set of linear equations for each K. The present broadening coefficients compared well with some of the prior measurements. [Copyright &y& Elsevier]

Self- and hydrogen-broadening coefficients and pressure-shift coefficients for the first overtone band transitions of 12C16O at room temperature have been determined through analysis of nine high-resolution (0.0055 cm−1) absorption spectra. These spectra were recorded using the 1-m Fourier transform spectrometer (FTS) at the McMath-Pierce facility of the National Solar Observatory on Kitt Peak, Arizona. Because of the short path length of the sample cell (10.0 cm), the volume mixing ratios of CO in hydrogen were relatively high, ∼18–22%, to achieve measurable absorption. These large volume-mixing ratios necessitated the simultaneous determination of the CO self-broadening and self-shift coefficients along with the hydrogen-broadening and hydrogen-induced shift coefficients. We have determined these coefficients at room temperature, along with line positions and absolute intensities, for the P(27) through R(27) 12C16O 2-0 transitions by fitting the entire spectral interval from 4130 to 4345 cm−1 in all nine spectra simultaneously using our multispectrum nonlinear least-squares procedure. Our intensity measurements are consistently low (1–6%) compared with the HITRAN values but the majority of the intensities are within 4% of the HITRAN values. The values of self-broadening coefficients vary from 0.0452 to 0.0862 cm−1 atm−1 at 296 K and those of hydrogen-broadening coefficient range between 0.0475 and 0.0795 cm−1 atm−1 at 296 K. All of our measured self- and hydrogen-shift coefficients are negative and range from −0.002 to −0.008 cm−1 atm−1. With the pressure and path length used in our study we did not find evidence of significant line mixing in either the self- or hydrogen-broadened spectra. This study represents the first high-resolution experimental determination of hydrogen-induced pressure broadening and pressure-shift coefficients in the 2-0 band of 12C16O at room temperature. [Copyright &y& Elsevier]