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

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