title: Relaxation matrix for symmetric tops with inversion symmetry: Line coupling and line mixing effects on NH3lines in the 𝝂4band.
abstract: Line shape parameters including the half-widths and the off-diagonal elements of the relaxation matrix have been calculated for self-broadened NH3lines in the perpendicular ν4band. As in the pure rotational and the parallel ν1bands, the small inversion splitting in this band causes a complete failure of the isolated line approximation. As a result, one has to use formalisms not relying on this approximation. However, due to differences between parallel and perpendicular bands of NH3, the applicability of the formalism used in our previous studies of the ν1band and other parallel bands must be carefully verified. We have found that, as long as potential models only contain components with K1= K2= 0, whose matrix elements require the selection rule Δk = 0, the formalism is applicable for the ν4band with some minor adjustments. Based on both theoretical considerations and results from numerical calculations, the non-diagonality of the relaxation matrices in all thePP,RP,PQ,RQ,PR, andRR branches is discussed. Theoretically calculated self-broadened half-widths are compared with measurements and the values listed in HITRAN 2012. With respect to line coupling effects, we have compared our calculated intra-doublet off-diagonal elements of the relaxation matrix with reliable measurements carried out in thePP branch where the spectral environment is favorable. The agreement is rather good since our results do well reproduce the observed k and j dependences of these elements, thus validating our formalism.
authors.affiliation: NASA/Goddard Institute for Space Studies and Department of Applied Physics and Applied Mathematics, Columbia University, 2880 Broadway, New York, New York 10025, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Ma
authors.affiliation: Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bât. 350, Campus d'Orsay F-91405, France.
authors.forename: C
authors.initials: C
authors.lastname: Boulet
authors.affiliation: Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487-0324, USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Tipping