Temperature dependence of N 2-broadened halfwidths of water vapor: The pure rotation and ν2 bands

Abstract

The temperature dependence of N 2-broadened halfwidths of H 2O has been studied over a temperature range of 200–1000 K to yield results applicable to atmospheric studies as well as hot sources. Forty-seven rotational transitions important to atmospheric studies were considered and the calculations were done for both the pure rotation and the ν 2 bands of water. The transitions span a range of J″ from 1 to 14 with the manifold of K″ a being sampled. The halfwidths were calculated using a cutoff-free theory with Anderson-Tsao-Curnutte interruption functions and trajectories correct to first order in time. Assuming the form γ(T) = γ(T 0)( T 0 T ) n, the exponent n has been determined for each transition. The results show strong fluctuations in n with the rotational quantum numbers and a lesser dependence on the particular vibrational band. The results give average temperature exponents for N 2 broadening of n( pure rotation) = 0.684 and n(ν 2) = 0.676 . Based on the results, an average value of n = 0.68 is recommended, and it is suggested that values calculated for specific rotational transitions be used when available.