Uniform Supersonic Expansion for FTIR Absorption Spectroscopy: The nu(5) Band of (NO)(2) at 26 K.

A high-resolution Fourier transform interferometer (Bruker IFS 120 HR) was combined with a uniform supersonic expansion produced by means of axisymmetric Laval nozzles. The geometry profile of the nozzle enabled us to work under precise thermodynamic and kinetic conditions. The effect of the cooling rate of different nozzles on cluster nucleation is illustrated. The experimental sensitivity was tested by recording the nu(5) band of (NO)(2) at 26 K. Copyright 2000 Academic Press.

Spectral Lineshape Parameters Revisited for HF in a Bath of Argon.

The test of an interaction potential for HF-argon recently determined from the spectroscopy of the Van der Waals complex requires accurate experimental widths and shifts cross sections. Since inconsistencies existed between previous measurements, collisional lineshapes were studied at T = 296 K by high-resolution Fourier transform spectroscopy for the 0-0, 0-1, and 0-2 bands. The accurate close-coupling molecular scattering calculations of Green and Hutson (1994. J. Chem. Phys. 100, 891) were extended to a complementary set of kinetic energies in order to check the thermal averaging procedure. Agreement between measured and computed room temperature cross sections is excellent for the three vibrational bands. This confirms the accuracy of the HF-argon surface and particularly its dependence on the HF vibrational level, which is sensitively probed both by the widths and by the shifts cross sections at high j(i) values. Copyright 1999 Academic Press.

Spectral Lineshape Parameters Revisited for HF in a Bath of Argon.

Previous measurements of asymmetries of the profiles of argon-broadened HF lines at moderate perturber densities (pressures higher than 10 atm) have been confirmed and extended by high-resolution Fourier transform spectroscopy. In some cases, the asymmetries observed here are of opposite sign when compared to the results obtained at much lower densities (pressures lower than 1 atm). By comparing all the available experiments, the competition between the various mechanisms leading to asymmetries has been analyzed as function of the perturber pressure and the vibrational transitions considered. Copyright 1999 Academic Press.

Line shape in the low frequency wing of self- and N(2)-broadened v(3) CO(2) lines: temperature dependence of the asymmetry.

The shape of the far wing of self- and N(2)-broadened CO(2) lines has been investigated in the 2150-2250-cm(-1) spectral region, i.e., on the low wavenumber side of the lines of the very intense v(3) band of (12)C(16)O(2) in a temperature range of atmospheric interest (200-300 K). The experimental results have been compared to calculated values based on the AFGL 1986 compilation. It appears that a symmetrical sub-Lorentzian line shape based on experiments made on the high wavenumber side cannot reproduce experiments. Comparison with experiments made at room temperature shows that the asymmetry of the correcting line shape factor chi strongly increases when decreasing the temperature.