Four spectra of methane in natural isotopic abundance in the 900-1050 cm-1 region were recorded using a Fourier transform spectrometer in Tomsk, Russia, with long optical paths 167 m and 1058 m at temperatures 28 and 51 degrees C. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and analyzed using effective Hamiltonian and effective dipole moment models. The enhanced absorption at long paths permitted to measure new transitions: in cold bands up to J max = 28 and in hot bands up to J max = 20. The new experimental line list contains line positions and intensities for 2570 features. Quantum assignments were made for 1246 lines of the main isotopologue 12 CH 4 . Comparisons of the theoretical absorption simulations with experimental spectra revealed a considerable improvement compared to the HITRAN2020 database. All assigned 1246 line positions were fitted to RMS standard deviations of 0.00065 cm-1 .

Potential energy surfaces (PES) of methane which are constructed using ten symmetrised combinations of four bond length and six interbond angles are referred to as (10S) PESs. At high energy ranges, it was found that (10S) PESs permitted improving by factor of five the fit quality of ab initio electronic energies of methane versus standard nine symmetric coordinates (9S) PES representations both in internal, orthogonal or normal-mode coordinates. We extend predictions of vibrational band origins to spectral range above 10,000 cm- 1 to help future analyses of experimental spectra. The accuracy at high energies is increased without notable deterioration at low-E levels (rms deviation of 0.26 cm- 1). Based on a comparison between various variants of (10S) PESs we expect that new theoretical band origins should have the accuracy not worse than 1-3 cm- 1 up to 13,400 cm- 1.

The form of the vibrational-rotational operator of kinetic energy for linear symmetric molecules of the A2B2 type in polyspherical nonorthogonal internal coordinates (bond lengths and angles between bonds) is obtained. Nonorthogonal coordinates have advantages in calculating the wave functions of heavy linear molecules, for example, C2F2 and C2Cl2; they also simplify the calculation of the intensity of vibrational-rotational spectral lines of molecules belonging to this type. This work is a continuation of work [1], in which the form of the kinetic energy operator in orthogonal coordinates was obtained. To verify the expressions derived, the lower vibrational-rotational energy levels of the acetylene molecule are calculated.

Four spectra of formaldehyde in natural isotopic abundance in the 3700-5200 cm-1 region were recorded at low temperature 160-166 K at Synchrotron SOLEIL for various pressures. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures in the range 3700-4450 cm-1 and analyzed using ab initio based effective Hamiltonian and line intensities computed using new ab initio dipole moment surface. A new measured line list contains positions and intensities for 6177 features. Refined parameters of effective Hamiltonian were fitted to all assigned line positions with the RMS deviations of 0.001 cm-1. Updated line lists include intensity values based on ab initio variational calculations which were subsequently empirically optimized. Comparison of our theoretical simulation with previously available data as well as with high-resolution and low-resolution experimental spectra are reported.

Four spectra of formaldehyde in natural isotopic abundance in the 3700-5200 cm(-1) region were recorded at low temperature 160-166 K at Synchrotron SOLEIL for various pressures. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures in the range 3700-4450 cm(-1) and analyzed using ab initio based effective Hamiltonian and line intensities computed using new ab initio dipole moment surface. A new measured line list contains positions and intensities for 6177 features. Refined parameters of effective Hamiltonian were fitted to all assigned line positions with the RMS deviations of 0.001 cm(-1). Updated line lists include intensity values based on ab initio variational calculations which were subsequently empirically optimized. Comparison of our theoretical simulation with previously available data as well as with high-resolution and low-resolution experimental spectra are reported.

Due to its major interest for the chemistry of planetary atmospheres and exobiology, accurate spectroscopy data of phosphine are required for the search of signatures of this molecule in astronomical observations. In this work, high resolution infrared laboratory spectra of phosphine were analyzed for the first time in the full Tetradecad region (3769-4763 cm-1) involving 26 rotationally resolved bands. Overall, 3242 lines were assigned in spectra previously recorded by Fourier transform spectroscopy at temperatures 200 K and 296 K, using a combined theoretical model based on ab initio calculations. The total nuclear motion Hamiltonian of PH3 including ab initio potential energy surface, was reduced to an effective Hamiltonian using the high-order contact transformation method adapted to vibrational polyads of the AB3 symmetric top molecules, followed by empirical optimization of the parameters. At this step, the experimental line positions were reproduced with a standard deviation of 0.0026 cm-1 that provided unambiguous identification of observed transitions. The effective dipole transition moments of the bands were obtained by fitting to the intensities obtained from variational calculations using the ab initio dipole moment surface. The assigned lines were used to newly determine 1609 experimental vibration-rotational levels up to Jmax = 18 with energy in the range 3896-6037 cm-1 that represents significant extension towards higher energies compared to previous works. Transitions for all 26 sublevels of the Tetradecad were identified but with noticeably fewer transitions for fourfold excited bands because of their weaker intensity. At the final step, pressure-broadened half widths were attached to each transition and a composite line list adopting ab initio intensities and empirical line positions corrected to the accuracy of about 0.001 cm-1 for strong and medium transitions was validated against experimental spectra available in the literature.

Four spectra of methane in natural isotopic abundance in the 4100-4300 cm(-1) region were recorded by using a Fourier transform spectrometer in Reims, France at long paths (202 m, 602 m, 1604 m and 1804 m) and different pressures. Additional spectra of (CH4)-C-12 covering the same region were obtained at 100-123 K for different pressures, 93 m path length at Synchrotron SOLEIL in Paris for different pressures and were used to measure low-J lines. Spectra of (CH4)-C-12 and (CH4)-C-13 obtained at 80 K at JPL in Pasadena were used for additional frequency calibrations. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and analyzed using effective Hamiltonian and effective dipole transition moment models. A new measured line list contains positions and intensities for 12,378 features. Quantum assignments were made for more than 11,520 new transitions, which represent similar to 99% of the integrated line intensity observed in this region. Some of 4556 hot band transitions for (Dyad - Tetradecad) system were assigned. The resulting list of lines is significantly more accurate than previous empirical compilations. All assigned 6963 line positions were fitted to RMS standard deviations of 0.0015 cm(-1). The sum of the observed intensities between 4100 and 4300 cm(-1) falls within 5% of the predicted value from ab initio variational calculations reported in the TheoReTS database (http: //theorets.univ-reims.fr ; http://theorets.tsu.u). (C) 2021 Elsevier Ltd. All rights reserved.

Results of the experimental study of the pressure dependence of self-broadening and shift of six isolated CO 2 absorption lines in the 1.6-μm spectral range at room temperature are presented. The measurements were carried out at a high-sensitivity high-resolution diode laser spectrometer with a signal-to-noise ratio of 3000 to 7000. To describe the experimental spectra, five line profile models VP, RP, qSDRP, qSDVP, and qSDVP + LM were used. A strong effect of weak closely spaced lines on the retrieved parameters (intensity and collisional broadening coefficient) of strong lines was found, as well as nonlinear pressure dependence of the narrowing parameter for the RP and qSDRP models. The linear pressure dependence of the parameters retrieved is shown for qSDVP + LM line profile in the pressure range from 0.001 to 1 atm.

Four spectra of normal samples of CH4 in the 4300-4600 cm(-1) region were recorded by using a Fourier transform spectrometer in Reims, France at long paths (202m, 602m, 1604m, and 1804m) and different pressures. Additional spectra of (CH4)-C-12 covering the same region were obtained at 80-123 K, and 93 m path length at SOLEIL Synchrotron in Paris for different pressures and were used to measure low-J lines. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and an- alyzed using effective Hamiltonian and effective dipole transition moment models. A new measured line list contains positions and intensities for 14,151 absorption features. Quantum assignments were made for more than 10,304 transitions of (CH4)-C-12, which represent -99% of the integrated line intensity observed in this region. Some 1699 hot band transitions for (Dyad - Tetradecad) system were assigned. The resulting list of lines is significantly more accurate than previous empirical compilations. Positions of 8605 cold band transitions for (GS - Octad) system were fitted with an RMS standard deviation of 0.0014 cm(-1). The sum of observed intensities between 4300 and 4600 cm(-1) fell within 8% of the predicted value from ab initio variational calculations reported in the TheoReTS database (http://theorets.univ-reims.fr;http://thearets.tsu.ru). (C) 2020 Elsevier Ltd. All rights reserved.

Three spectra of normal samples of CH4 in the 8850-9180 cm(-1) region were recorded at temperatures 296 K, 254 K, 208 K by using a Fourier transform spectrometer in Tomsk with the cell path of 2.2 m. Additional spectra of (CH4)-C-12 covering the same spectral range were obtained at 108 K with the cell path of 0.2 m. The lower energy levels were corrected for 1029 lines available in the HITRAN [1] database in this range. Additionally, 275 new quantum assignments were added using ab initio variational calculations combined with the spectra analyses based on effective Hamiltonian and effective dipole transition moment fits. Simulations of observed spectra show that new line list is much more accurate for lower temperatures than the previous compilation included in HITRAN-2016. Finally, the lower state energies are provided for 1304 transitions that represents similar to 66% of the integrated line intensity observed in this region at 296 K. The sum of observed intensities between 8850 and 9180 cm(-1) agree within 7% to the predicted value of ab initio variational calculations reported in the TheoReTS database (http://theorets.univ-reims.fr; http://theorets.tsusu). (C) 2019 Elsevier Ltd. All rights reserved.

A new study of (CH4)-C-12 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 CH4 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 (CH4)-C-12 was used for low-J line positions. Another 80 K spectrum of enriched (CH4)-C-13 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 similar to 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). (C) 2018 Elsevier Ltd. All rights reserved.

The paper considers the artificial corrections of measured gas pressures and wavenumber scale shifts for multispectrum fit by the example of R(22) carbon dioxide self-broadened line of 30013 <- 00001 vibrational band. For this purpose the two quadratic and hypergeometric speed-dependent Voigt line profile models including line mixing within the (Rosenkranz) first-order approximation for line-coupling effects with linear dependences of corresponding model parameters on pressure were applied. The intercomparison of the retrieved results only for pressure corrections, only for wavenumber scale shifts, for both together, and for no correction case demonstrates considerable disagreement between them. The most significant differences in parameters, retrieved in such a way, belong to the first-order line-mixing coefficients and are caused mostly by the shift scattering of wavenumber scale at different pressures. (C) 2015 Elsevier Inc. All rights reserved.

Experimental spectra of pure water vapor and its mixtures with N2 and He were measured in a pressure range (4–19 for pure H2O and 70–630mBar for H2O diluted in N2 and Ne) by the diode laser spectrometer between 7184 and 7186cm−1. The noise equivalent absorption cross-section of the all observed spectra varied from 1.2 to 4.3×10–24cm2/molec allowing signal to noise ratio from 10 for weak (intensity on the order of 5×10–25cm/molec at 296K) to 15,000 for strong (intensity on the order of 6×10–22cm/molec) spectral lines respectively. The Voigt, Galatry, and Speed-dependent Voigt (SDV) profiles were used to fit the experimental spectra. This region includes 7 absorption lines of H2O and one HDO line according to the new line lists of H2O. Line positions, intensities, line shift, collisional broadening and narrowing coefficients for 6 spectral lines were retrieved by multispectrum fitting procedure assuming the linear pressure dependence. The spectral parameters of the doublet (ν1+ν3; 660←661; 661←660) at 7185.596cm−1 were determined for the first time.

Numerical calculations of the ratio of line width and maximum value of two speed-dependent Voigt line profiles to the respective values of their speed-independent analogs are performed in the high-pressure limit. The intercomparison demonstrates considerable disagreement between different speed-dependent models. (C) 2013 Elsevier Inc. All rights reserved.

The experimental spectra of CH4 absorption lines in the spectral region of 6105–6107cm−1 have been measured in binary mixtures with N2 and Ne by a high-resolution photo-acoustic laser spectrometer. Lineshape models, including Dicke narrowing and speed dependent effects were used to CH4 spectral line (ν0=6105.62573cm−1) fitting. The hard-, soft-collision and speed dependence models lead to better fits of experiments than the Voigt profile, but the systematic residuals and biases in the retrieved line parameters are remained.

The results of the investigation of absorption spectra of the methane R5 multiplet of 2ν 3 band, broadened by nitrogen, are presented. The absorption spectra of the methane-nitrogen mixture (CH4:N2 = 1:113.36) were recorded, using a two-channel photometric spectrometer, based on a tunable diode laser. The multispectrum least-squares fitting procedure was applied to all experimental spectra, recorded at different pressures, using the program, developed at IAO SB RAS (Protasevich, 2011). The program is based on a relatively simple line-profile model proposed in Pine (J. Quant. Spectrosc. Radiat. Transf. 57:145, 1997) and linear pressure dependence of the line-profile parameters. The line center positions, intensities, broadening, shifting, and mixing coefficients were determined for four lines of the methane R5 multiplet. The results have been compared with other available data.

A high-sensitive two-channel photo-acoustic (PA) spectrometer with a near infrared diode laser was used to make precise measurements of N2-broadened methane spectra in the R9 multiplet of 2ν3 band. For the accurate retrieval of spectroscopic line parameters (intensities, positions at zero pressure, pressure-shifting and -broadening, collisional narrowing and line mixing coefficients) from the methane PA spectra, a program based on a multispectrum fitting procedure has been used. The multispectrum least squares fitting procedure is based on a relatively simple line profile model and on the linear pressure dependences of the line profile parameters. The line parameters were determined for 11 lines of the methane 2ν3 R9 multiplet. The results have been compared with other available data.

Mathematical expressions for the shape and amplitude of a photoacoustic signal generated due to the multiphoton absorption of Gaussian laser pulses are derived. It was found that the sensitivity of a photoacoustic spectrometer increases in proportion to n(3/4) when changing from one-photon linear absorption to nonlinear multiphoton absorption, where n is the nonlinearity exponent. Calibration of the photoacoustic spectrometer used in the measurements of multiphoton absorption cross sections is discussed.

The transformation of the integration domain upon passage from the variables impact distance-initial relative velocity to the variables closest approach distance-initial relative velocity in the Robert-Bonamy method for an arbitrary isotropic potential is considered. As an example, the result obtained is applied to the Lennard-Jones potential.

General expressions for fourth-order terms for calculating the interruption function S ( b ) in terms of the perturbation theory are derived for molecules with different symmetry properties and arbitrary trajectories of the relative motion of colliding molecules. An expression for a quadruple integral over time appearing in the definition of new resonance functions is written in terms of the Fourier transform of the coefficients of the intermolecular interaction potential.