R. Lynch

New developments in the theory of pressure-broadening and pressure-shifting of spectral lines of H2O: The complex Robert-Bonamy formalism

Abstract Calculations of the halfwidth and line shift of water vapor perturbed by N2, O2, CO2, and H2 based on a complex implementation of the formalism of Robert and Bonamy are made. The potentials employ the leading terms of the electrostatic potential, a Lennard -Jones (6–12) atom-atom potential, and the induction and dispersion components of the isotropic potential. The dynamics of the collisions are correct to second order in time. The results are compared with measurements and very good agreement is observed for both halfwidths and line shifts. A new feature in this approach is that the real and imaginary components of the S matrix affect both the halfwidth and the line shift. It is shown here that the imaginary parts of the S matrix strongly affect the calculated halfwidths for some of the systems considered.

Fully Complex Implementation Of The Robert-bonamy Formalism: Half Widths And Line Shifts Of H2O Broadened By N2

The complex semiclassical formalism of Robert and Bonamy is used to calculate both half widths and line shifts for water vapor in a bath of nitrogen. The assumed intermolecular potential is a combination of electrostatic, Lennard‐Jones 6‐12 atom–atom, induction, and dispersion terms. The complex valued resonance functions have been previously evaluated when the assumed potential was electrostatic only. In this work these functions are evaluated when the potential is extended to include the atom–atom terms. Calculations made in the 3ν1+ν3 vibrational band of H2O are in good agreement with experimental results for both the half width and line shifts. It is shown that the imaginary parts are important for both the line shift and half width calculations.

Theoretical calculations of pressure broadening coefficients for H2O perturbed by Hydrogen or helium gas

Abstract To aid in the reduction of remote-sensing data from the outer planets, collision-broadened halfwidths are calculated for water vapor broadened by H2 and are estimated for He-broadening. The model used is a fully complex implementation of the Robert and Bonamy formalism with parabolic trajectories and all relevant terms in the interaction potential. Calculations are performed for 386 pure rotational transitions of H2O with J″ = 0 to 14 and Ka″ = 0 to 8. In addition, the temperature dependence of the halfwidth is computed for a temperature range from 200 to 750 K for 33 transitions with J″ = 1 to 10 and Ka″ = 0 to 8. The calculations are compared with known measurements of pure rotational and v2 lines and good agreement is observed (−2 and −4% difference respectively). Finally, methods for estimating halfwidths for H2- and He-broadening are presented.

Pressure‐induced widths and shifts for the ν3 band of methane

Widths and shifts of methane lines perturbed by nitrogen are calculated using a complex‐valued implementation of Robert–Bonamy (RB) theory. The static intermolecular potential is described as a sum of electrostatic forces and Lennard‐Jones (6‐12) atom–atom terms, using literature values for all physical parameters. Vibrational dependence of the isotropic potential is obtained from the polarizability of methane assuming a dispersion interaction. The repulsive part of the Lennard‐Jones accounts for the greatest part of widths, while dispersion interactions are largely responsible for shifts. Although the average error between calculated and observed linewidths (up to J=8) is less than 6%, their distribution suggests the influence of interactions not described in the present theory.

HALFWIDTHS AND LINE SHIFTS OF WATER VAPOR BROADENED BY CO2 : MEASUREMENTS AND COMPLEX ROBERT-BONAMY FORMALISM CALCULATIONS

Measurements of CO2-broadened line shifts of 29 transitions belonging to the v1, 2v2 and v3 bands of water vapor are made at T = 294.4 K. The halfwidths of 31 transitions were previously reported [R. R. Gamache et al (1995)]. Calculations of the halfwidth and line shifts based on a fully complex implementation of the formalism of Robert and Bonamy are made for these transitions. The calculations employ an electrostatic, Lennard-Jones (6–12) atom-atom, and isotropic induction and dispersion components of the potential and dynamics correct to second order in time. The results are compared with the measured values and very good agreement is observed for both halfwidths and line shifts. A new feature in this approach is that the real and imaginary components of the S matrix affect both the halfwidth and the line shift. It is shown here that the imaginary parts of the S matrix strongly affect the calculated H2OCO2 halfwidths.