Theoretical calculation of CH 3Br/N 2-broadening coefficients at various temperatures

Abstract

The N 2-broadening coefficients of CH 3 79Br and CH 3 81Br have been calculated for transitions belonging to the P P-, P Q-, P R-, R P-, R Q- and R R-branches of the ν 6 band near 10 μm, using a semiclassical impact theory. The intermolecular potential used, includes in addition to the overwhelming electrostatic interactions, induction and dispersion energy contributions, which are significant only for low J transitions with K approaching or equal to J. Comparisons have been performed with the extensive set of previous measurements at room temperature [4]. The theoretical results are in satisfactory agreement with the experimental data, and the J and K dependences are reasonably well reproduced. From calculations at 200, 230, 260 and 296 K, the temperature exponent of the collisional broadenings derived from a simple power law has been determined for each transition of each sub-branch and compared with a recent experimental evaluation [5]. Finally the N 2-broadening coefficients calculated at 296 K and their temperature exponents are given as supplementary materials of this paper for atmospheric applications and databases.