N2-, O2- and He-collision-induced broadening of sulfur dioxide ro-vibrational lines in the 9.2 µm atmospheric window.

Sulfur dioxide (SO2) is a molecule of considerable interest for both atmospheric chemistry and astrophysics. In the Earth's atmosphere, it enters in the sulfur cycle and it is ubiquitous present in polluted atmospheres, where it is responsible for acid rains. It is also of astrophysical and planetological importance, being present on Venus and in interstellar clouds. In this work the collisional broadening of a number of ν1 ro-vibrational lines of SO2 perturbed by N2, O2 and He are investigated at room temperature in the 9 µm atmospheric region by means of high resolution tunable diode laser (TDL) infrared spectroscopy. From N2- and O2-broadening coefficients, the broadening parameters of sulfur dioxide in air, useful for atmospheric applications, are derived as well. From the present measurements some conclusions on the quantum number dependence of the N2-, O2- and He-broadening coefficients are drawn. While the J dependence is weak for all the perturbers investigated, different trends with Ka are reported. N2-broadening coefficients show a slight decrease with increasing values of Ka, whereas O2 and He broadening cross sections first increase up to Ka(″)≈6 and then they keep a nearly constant value. A comparison and a brief discussion on the efficiency of self-, N2-, O2- and He-collisional dynamics are given. The data obtained represent a significant analysis on foreign broadening of SO2 useful for atmospheric remote sensing and astrophysical applications.

Toward a complete understanding of the vinyl fluoride spectrum in the atmospheric region.

A deep and comprehensive investigation of the vinyl fluoride (CH(2)CHF) spectrum in the atmospheric window around 8.7 µm is presented. At first, the ro-vibrational patterns are modelled to an effective Hamiltonian, which also takes into account the coupling of the C-F stretching vibration, ν(7), with the neighbouring vibrational combination ν(9)+ν(12). The obtained Hamiltonian gives very accurate simulations and predictions of the ro-vibrational quantum energies. Then, in the main part of the work, an experimental and theoretical study of vinyl fluoride self-broadening collisions is carried out for the first time. The broadening coefficients obtained experimentally are compared with those calculated by a semiclassical theory, demonstrating a significant contribution of collisional coupling effects between lines connecting pairs of degenerate (or nearly degenerate) rotational levels. Finally, the experimentally retrieved integrated absorption coefficients are used to calculate the absorption cross-section of the ν(7) normal mode, from which dipole transition moments are derived. The obtained results provide a deep insight into the spectral behaviour of vinyl fluoride, in a spectral region of primary relevance for atmospheric and environmental determinations. Indeed, the data presented constitute an accurate model for the remote sensing of vinyl fluoride--a molecule of proved industrial importance which can lead to hazardous effects in the atmosphere and affects human's health.

Experimental and theoretical study of the broadening and shifting of N2H+ rotational lines by helium.

Pressure broadening and pressure shift of N(2)H(+) rotational lines perturbed by collisions with He are studied for the first time using experiment and theory. Results are reported from measurements at 88 K for the rotational transitions j = 3<--2, 4<--3, 5<--4 and 6<--5 with frequencies ranging from 0.28 to 0.56 THz. The agreement between experiment and theoretical data derived from close coupling calculations confirms the reliability of a theoretical framework used for state-to-state transition rates of interest in the interpretation of spectroscopic data from interstellar molecular clouds. The influence of hyperfine effects on shifts and widths of the rotational lines is discussed in detail. Although in principle possible, experiment and theoretical considerations lead to the conclusion that hyperfine effects only play a minor role.

Spectroscopic measurements of SO(2) line parameters in the 9.2 mum atmospheric region and theoretical determination of self-broadening coefficients.

Sulfur dioxide is still the subject of numerous spectroscopic studies since it plays an active role in the chemistry of Earth's atmosphere and it is a molecule of proven astrophysical importance. In the present work we have determined the self-broadening and integrated absorption coefficients for several lines in the nu(1) band spectral region around 9.2 mum. Besides the parameters of the lines belonging to the nu(1) fundamental of (32)SO(2), also those for some rovibrational lines of the nu(1)+nu(2)-nu(2) hot band of the (32)SO(2) isotopologue and the nu(1) band of the (34)SO(2) isotopic species have been determined. The measurements have been carried out at 297 K using a tunable diode laser spectrometer. The self-broadening parameters have also been theoretically determined employing a semiclassical formalism based on the Anderson-Tsao-Curnutte approximation. The study has been completed with the determination of the vibrational cross sections of the three fundamental bands measured from the spectra recorded at a resolution of 0.2 cm(-1) using a Fourier transform infrared spectrometer.

Experimental and theoretical study of helium broadening and shift of HCO+ rotational lines.

An experimental and theoretical study of pressure broadening and pressure shift of HCO(+) rotational lines perturbed by collisions with He is presented. Results are reported from measurements at 88 K for the lines j=4<--3, 5<--4 and 6<--5 with frequencies ranging from 0.35 to 0.54 THz. Using a new CCSD(T)/aug-cc-pVQZ potential energy surface for the He-HCO(+) interaction, the collisional line shape parameters are studied from fully quantum and semiclassical calculations. Results from the quantum treatment are in satisfactory agreement with experiments whereas the semiclassical approach can lead to appreciable differences. A study of the dependence of line width Gamma and shift s as a function of the translational energy shows the presence of quantum oscillations. Calculations on a previous Hartree-Fock-based potential energy surface lead to quite similar results for the collisional line shape parameters. Using a simplified version of the potential morphing method it is found that the line width Gamma is particularly sensitive to the long-range part of the potential energy surface. This also explains the success of the first line-broadening calculations which date back to the 1950s.

New experimental and theoretical results for argon broadening and shift of HCO+ rotational lines.

An experimental and theoretical study of the pressure broadening and the pressure shift of three HCO(+) rotational lines (j=4<--3, 5<--4 and 6<--5) perturbed by collisions with Ar is presented. The measurements are carried out at 77 K and are compared to close-coupling calculations performed on an accurate potential energy surface for the Ar-HCO(+) interaction extending from small to very large separations between the ion and the perturber. For the pressure broadening, agreement between experiment and theory is satisfactory for both close-coupling and semiclassical calculations. For the pressure shift, however, close-coupling calculations are superior. The results agree with experiment in sign and order of magnitude, while semiclassical calculations are inaccurate for the shift of the presently studied lines because they neglect the contribution of strong collisions.