Pressure broadening and shifting of vibrotational lines of atmospheric gases

Abstract

Water vapour is one of the strongest absorbers of radiation in the Earth's atmosphere, but some other gases also play an important role in the atmospheric radiative transfer processes: carbon dioxide CO 2 , carbon monoxide CO, ozone О 3 , methane CH 4 . Minor atmospheric pollutants such as hydrogen sulphide H 2 S, methyl fluoride CH 3 F, methyl chloride CH 3 Cl, ethylene C 2 H 4 , nitric oxide NO, nitrous oxide N 2 O and nitrogen dioxide NO 2 are equally recognised for their implication in the fundamental chemical reactions occurring in the terrestrial atmosphere. As a consequence, a lot of spectroscopic studies are made for these molecules in order to obtain the line positions, intensities and widths. They are briefly summarised below, starting by asymmetric waterlike molecules of X 2 Y-type which have the same selection rules for vibrotational spectra. Vibrotational lines of asymmetric X 2 Y moleculesBetween asymmetric tops of the X 2 Y type most attention in the spectroscopic literature is paid to the H 2 S, SO 2 , O 3 and NO 2 molecules. _________________________________________________________________ A vibrotational state (v 1 v 2 v 3 ) [J K a K c ] of these molecules is characterised by three vibrational quantum numbers v 1 , v 2 , v 3 and three rotational quantum numbers J, K a , K c . In the NO 2 molecule, having an unpaired electron (total electronic spin S = 1/2), each vibrotational level is split by the spin-rotational interaction into two components (J = N ± S) denoted by + or -, and the three rotational quantum numbers are N, K a , K c . For a given set of vibrotational quantum numbers the corresponding energies are obtained by a diagonalization of the effective Hamiltonian matrix of Eq. (3.