Modified Complex Robert-Bonamy (MCRB) calculations of H2O transitions broadened by H2 for applications to planetary and exoplanet atmospheres

Abstract

Line shape parameters for hydrogen broadening of water vapor are needed to understand remote sensing measurements of planetary and exoplanet atmospheres. In order to address these needs, semiclassical calculations based on the Modified Complex Robert-Bonamy (MCRB) formalism were made. The intermolecular potential for the calculation is comprised of electrostatic, atom-atom (expanded to order 16 and rank 4), induction, and London dispersion terms. The trajectories were determined by numerical integration of the Hamilton’s equations. The average over the Maxwell–Boltzmann distribution of velocities was performed by integration over 35 velocities corresponding to the temperature range 75K – 27000K. The formalism is complex valued yielding the half-width and line shift from a single calculation. The calculations are reported at 7 temperatures from 200 to 700 K. The half-width temperature dependence coefficient n was determined using the relation γ(T) = γ(T)[T0/T]n with T0=296K. The calculations are compared with the measurements of Brown and Plymate [JQSRT 56, 263, 1996]. Future plans for further refinement of the intermolecular potential are discussed.