J.P. Champion

The 1997 spectroscopic GEISA databank

The current version GEISA-97 of the computer-accessible database system GEISA (Gestion et Etude des Informations Spectroscopiques Atmospheriques: Management and Study of Atmospheric Spectroscopic Information) is described. This catalogue contains 1,346,266 entries. These are spectroscopic parameters required to describe adequately the individual spectral lines belonging to 42 molecules (96 isotopic species) and located between 0 and 22,656 cm-1. The featured molecules are of interest in studies of the terrestrial as well as the other planetary atmospheres, especially those of the Giant Planets. GEISA-97 contains also a catalog of absorption cross-sections of molecules such as chlorofluorocarbons which exhibit unresolvable spectra. The modifications and improvements made to the earlier edition (GEISA-92) and the data management software are described. GEISA-97 and the associated management software are accessible from the ARA/LMD (Laboratoire de Meteorologie Dynamique du CNRS, France) web site: http://ara01.polytechnique.fr/registration.

Spherical top data system (STDS) software for the simulation of spherical top spectra

Abstract The Spherical Top Data System (STDS) software package for the simulation of spherical top spectra is presented. It consists of a single UNIX script with self-explanatory arguments allowing the non-expert user to calculate spectra from the results of the high resolution analyses performed over the recent decades on this type of molecules. More than one hundred parameter files are presently available including various band systems of 16 molecular species (among which methane is the most documented) and various types of calculations: rovibrational energy levels, i.r. absorption, Raman scattering and Stark coefficients. STDS is freely accessible by anonymous ftp at jupiter.u-bourgogne.fr. The basic instructions to get, install and execute STDS are explained. The current status of the STDS content is described.

Methane line parameters in HITRAN

Abstract Two editions of the methane line parameters (line positions, intensities and broadening coefficients) available from HITRAN in 2000 and 2001 are described. In both versions, the spectral interval covered was the same (from 0.01 to 6184.5 cm −1 ), but the database increased from 48,033 transitions in 2000 to 211,465 lines in 2001 because weaker transitions of 12 CH 4 and new bands of 13 CH 4 and CH3D were included. The newer list became available in 2001 in the “Update” section of HITRAN. The sources of information are described, and the prospects for future improvements are discussed.

Vibration-rotation energies of harmonic and combination levels in tetrahedral XY4 molecules: Theory and extrapolation method

Abstract This paper presents a general method for studying overtones and combination bands of tetrahedral XY4 molecules. Making full use of group theory, the matrix representation of the Hamiltonian restricted to any set of vibrational sublevels is easily derived from a basis of rovibrational matrices. Explicit expressions for the reduced matrix elements are developed for all the operators of any order occurring in states for which Σs vs ≤ 2, including any interaction type. The parameters introduced are directly the Hamiltonian expansion coefficients and consequently have the same physical significance in any vibrational state. The treatment of overtones and combination bands for which the corresponding fundamentals are analyzed is considered in detail. In this case, the parameters of the ground and fundamental states remain fixed and only a few new parameters occurring specifically in the studied state need to be determined. In this way, the convergence of least-squares fits is greatly improved. The example of methane is used to illustrate the efficiency of this method suitable for the direct determination of potential constants.

The MIRS computer package for modeling the rovibrational spectra of polyatomic molecules

Abstract The MIRS spectroscopic software for the modeling of ro-vibrational spectra of polyatomic molecules is presented. It is designed for the global treatment of complex band systems of molecules to take full account of symmetry properties. It includes efficient algorithms based on the irreducible tensor formalism. Predictions and simultaneous data fitting (positions and intensities) are implemented as well as advanced options related to group theory algebra. Illustrative examples on CH 3 D, CH 4 , CH 3 Cl and PH 3 are reported and the present status of data available is given. It is written in C ++ for standard PC computer operating under Windows. The full package including on-line documentation and recent data is freely available at the URL: http://www.u-bourgogne.fr/LPUB/MIRS.html .

Rotational analysis of vibrational polyads in tetrahedral molecules: Simultaneous analysis of the pentad energy levels of 12CH4

Abstract A theoretical model for the rovibrational analysis of clustered vibrational states for tetrahedral molecules is presented. The results of a comprehensive study of the five bands ν1, ν3, 2ν2, ν2 + ν4, and 2ν4 of 12CH4 are reported. The Hamiltonian has been developed to the third order in the Amat-Nielsen classification. Twenty-two parameters related to the ground state and the dyad ν 2 ν 4 have been transferred unchanged and 52 new parameters have been adjusted to fit experimental data, mainly interferometric ir data in the region 2250–3250 cm−1. The analysis has been realized through J′ = 18 involving 1919 observed upper-state energies. The overall standard deviation of the fit is 0.022 cm−1. A prediction of upper-state energies for the five bands has been carried out through J′ = 20. The model reproduces qualitatively and quantitatively the rotational fine structure of the upper levels in the full range of J′ values including level crossings (J′ ≥ 12), for the first time. The problem of higher excited vibrational states in methane is briefly discussed.

Experimental and theoretical study of line mixing in methane spectra. I. The N2-broadened ν3 band at room temperature

Line-mixing effects have been studied in the ν3 band of CH4 perturbed by N2 at room temperature. New measurements have been made and a model is proposed which is not, for the first time, strictly empirical. Three different experimental set ups have been used in order to measure absorption in the 2800–3200 cm−1 spectral region for total pressures in the 0.25–2 and 25–80 atm ranges. Analysis of the spectra demonstrates the significant influence of line mixing on the shape of the Q branch and of the P and R manifolds. A model is proposed which is based on state-to-state collisional transfer rates calculated from the intermolecular potential surface with a semiclassical approach. The line-coupling relaxation matrix is constructed from these data and two additional parameters which are fitted on measured absorption. Comparisons between measurements and spectra computed accounting for and neglecting line mixing are made. They prove the quality of the approach which satisfactory accounts for the effects of press...

Analysis of the ν2ν4 dyad of 12CH4 and 13CH4

Abstract The reanalysis of the ν 2 ν 4 dyad of 12CH4 and the first detailed analysis of the same dyad of 13CH4 have been carried out using new infrared measurements combined with previously published microwave data. The line positions of the ν 2 ν 4 dyad near 7 μm have been measured with a precision of 0.00006 cm−1 using 0.0055 and 0.011 cm−1 resolution spectra recorded with the Fourier Transform spectrometer at Kitt Peak National Observatory/National Solar Observatory. Using a sixth order reduced Hamiltonian, the ground state and the ν 2 ν 4 upper state parameters have been adjusted simultaneously. Standard deviations of 0.065 10−3 cm−1 involving data through J = 23 for 12CH4 and 0.062 10−3 cm−1 involving data through J = 19 for 13CH4 have been obtained. Over 7100 infrared transitions of methane (with strengths greater than 10−6 cm−2 atm−1 at 296 K in natural isotopic abundance) have been calculated. The majority of the predicted line positions have individual standard deviations of 10−4 cm−1 or better.

The vibrational ground state of 12CH4 and 13CH4

Abstract Improved ground state constants of 12 CH 4 and 13 CH 4 have been obtained using new infrared measurements combined with previously published microwave data. The line positions of the ν 2 ν 4 dyad near 7 μm have been measured with a precision of 0.00006 cm −1 using 0.0055 and 0.011 cm −1 resolution spectra recorded with the Fourier transform spectrometer at Kitt Peak National Observatory/National Solar Observatory. Using a sixth order Hamiltonian, the ground state and the ν 2 ν 4 upper states (J. P. Champion, J. C. Hilico, C. Wenger and L. R. Brown, J. Mol. Spectrosc. 133, 256–272 (1989)) have been fitted simultaneously to within the precision of the data through J = 23 for 12 CH 4 and J = 19 for 13 CH 4 . Absolute ground state energies and their standard deviations are given up to J = 30 for both isotopes. For Q - and R -branch transitions within the ground states, the statistical precisions from this study are similar (in the same order of magnitude) to the precision of microwave measurements.

Parameters of reduced Hamiltonian and invariant parameters of interacting E and F2 fundamentals of tetrahedral molecules: ν2 and ν4 bands of 12CH4 and 28SiH4

Abstract The problem of unambiguous processing of experimental data for interacting doubly and triply degenerate states of tetrahedral molecules is studied on the basis of 85 fits of ν2 and ν4 spectra of 12CH4 and 28SiH4. The formalism of irreducible tensors of the paper by J. P. Champion and G. Pierre [J. Mol. Spectrosc. 79, 255–280 (1980)] is used. The behavior of correlated parameters of the Hamiltonian expansion is examined first by series of actual fits of experimental data. It is shown that any of the q2J2- or q2J3-type parameters of the ν 2 ν 4 dyad may be given positive or negative or zero values without deterioration of the quality of fits. The other parameters move along trajectories which are described by PTZ equations [V. I. Perevalov, Vl. G. Tyuterev, and B. I. Zhilinskii, Chem. Phys. Lett. 104, 455–461 (1984)] with an accuracy of better than 5% (in the case of CH4). The experimental values of PTZ coefficients are determined. The nonlinear trajectories relating the isolated state and the interacting state models are presented as well. In order to achieve unambiguous fits the properties of the reduced Hamiltonian are studied in detail considering the influence of removing various terms from the Hamiltonian on the correlation matrix and on the standard deviation of fits σ. Twenty parameters of the reduced Hamiltonian are determined which reproduce 698 energy levels of ν 2 ν 4 of CH4 up to J = 20 with the experimental accuracy = 0.003 cm−1. Invariant q2J2-type parameters are introduced, and their values are determined for ν 2 ν 4 of 12CH4 and 28SiH4. Attention is paid to the fact that the latter approach would enable one to determine an unambiguous physically meaningful set of spectroscopic parameters and simultaneously achieve the absolute minimum of σfit.