N. Lacome

Phosphine spectrum at 4–5 μm: Analysis and line-by-line simulation of 2ν2, ν2 + ν4, 2ν4, ν1, and ν3 bands

Abstract The five absorption bands of PH3 at 4–5 μm, i.e., 2ν2, ν2 + ν4, 2ν4, ν1, ν3, were simultaneously analyzed from FT spectra recorded with an apodized resolution of 0.0054 cm−1. A theoretical model suited to the strong vibro-rotational couplings among the five bands was used. More than 4400 transitions (J ≤ 16) pertaining to the five bands were assigned in the range 1885–2445 cm−1, but only 3766 relatively unblended transitions were finally retained for the adjustment of the upper state energy parameters. A set of 57 energy parameters was required to reproduce the experimental wavenumbers with an overall standard deviation of 0.009 cm−1, consistent with the estimated upper limit of uncertainty when taking into account all factors of experimental errors. Absolute intensities of about 1600 lines were also measured, mainly in 2ν2, ν2 + ν4, and 2ν4 bands. The fitting of these data was achieved by using a restricted set of 53 energy parameters which yields the best compromise for both spectral position and intensity analyses. An estimate was then obtained for the four dipole moment derivatives involved in 2ν2, ν2 + ν4, and 2ν4, allowing us to reproduce the intensity measurements with an overall standard deviation of 10.9%, consistent with the experimental uncertainties. Absolute bandstrengths relative to 2ν2, ν2 + ν4, and 2ν4 were thus derived for the first time. Last, a line-by-line simulation of the five bands (J ≤ 16) was carried out in a form suitable for planetary applications. PH3, which is observed in Jupiter and Saturn, is an important molecule for studies of their atmospheric structures. The 5-μm bands are of special importance because the atmospheres are sounded deep at these wavelengths.

The NO Dimer.

Spectra of the symmetric nu1 vibration of the NO dimer have been recorded in gas phase at low temperature, with a high-resolution infrared Fourier transform spectrometer. All the lines were least-squares fitted to a Voigt profile convoluted with the well-known apparatus function of the spectrometer. By means of this method, the frequencies of more than 109 new lines were measured. From the intensities of a set of 33 well-fitted and completely isolated lines, the transition moment was extracted. NO-broadening coefficients of the dimer lines were also measured as well as the predissociation time, which was found to be (2.65 +/- 0.53) ns. Copyright 1999 Academic Press.

High resolution Fourier transform infrared spectroscopy of the ν6 and ν10 bands of jet‐cooled Fe(CO)5

Rovibrational FTIR spectra of Ni(CO)4 and Fe(CO)5 have been recorded in supersonic argon expansions at resolutions up to 0.004 cm−1. Rotational temperatures as low as 4 K for the ν6 band of Fe(CO)5 and 6 K for the ν5 band of Ni(CO)4 have been determined from the populations of the rotational levels, and an efficient vibrational cooling has been evidenced by the large reduction of hot band absorptions. An analytical model including the instrumental line shapes and the intensity distribution is proposed to enable simulations of overlapping rovibrational transitions of symmetric top molecules. The spectroscopic study of the ν6 and ν10 stretching bands of Fe(CO)5 yielded the following parameters (3σ uncertainties in parenthesis): ν0=2038.106 97(91) cm−1, B6=0.026 797(12) cm−1, and B0=0.026 826(10) cm−1 for the 610 transition, ν0=2015.5513(12) cm−1, ΔA10=−0.000 086(5) cm−1, B10=0.026 786(4) cm−1, and ξ10=−0.049(3) for the 1010 transition based on the literature value of A0.

Line intensities of acetylene: Measurements in the 2.5-μm spectral region and global modeling in the Δp=4 and 6 series

Abstract More than 670 line intensities of nine perpendicular bands of acetylene are measured in the 2.5-μm spectral region using a step-by-step interferometer. Absolute values of line intensities are obtained with an average accuracy of 5%. Vibrational transition dipole moment and Herman–Wallis coefficients are determined for each studied band. These measured line intensities, and those previously measured in the 3.8-μm region [Jacquemart D, Lacome N, Mandin JY, Dana V, Lyulin OM, Perevalov VI. Multispectrum fitting of line parameters for 12C2H2 in the 3.8-μm spectral region. JQSRT, submitted for publication], are treated simultaneously within the framework of the effective operators approach. The sets of effective dipole moment parameters obtained reproduce the observed line intensities within the experimental uncertainty. The good predictive ability of the modele is demonstrated.

SIMPLE MODELLING OF Q-BRANCH ABSORPTION. II: APPLICATION TO MOLECULES OF ATMOSPHERIC INTEREST (CFC-22 AND CH3CL)

Abstract The simple approach developed in a previous paper in order to model absorption by Q-branches is applied to the 2v6 Q-branch of CFC-22 perturbed by N2 and to the v5R Q0-branch of CH3Cl perturbed by He. Measurements have been made for these two systems at room temperature for a number of pressures in the 0.05–1.00 atm range. It is shown that our model enables satisfactory prediction of both the pressure and wavenumber dependences of absorption with only six effective parameters; the latter, which depend on temperature only, have been deduced from measured spectra. There values are in satisfactory agreement with results from other sources, except for the average broadening parameter, which is generally underestimated with the model as explained in our previous paper.