N2 and O2 induced halfwidths and line shifts of water vapor transitions in the (301)←(000) and (221)←(000) bands

Abstract

Using a complex version of Robert–Bonamy theory (CRBF), the role of the intermolecular potential in the pressure broadening of water perturbed by nitrogen and oxygen is studied. Investigation focuses on questions surrounding the convergence of calculated line widths, i.e., (i) why certain spectral lines are more sensitive than others to short-range interactions, and (ii) whether converged calculations containing short-range interactions represent an improvement over other treatments. Comparison with a large number of experimentally determined halfwidths and line shifts in the (301)←(000) and (221)←(000) bands is provided. It is found that the atom–atom component of the intermolecular potential plays an important role in determining the halfwidth and line shift. To obtain good agreement with measurement, the atom–atom potential needs to be expanded to at least eighth order for all water vapor transitions broadened by oxygen and many broadened by nitrogen.