A far wing line shape theory and its application to the foreign-broadened water continuum absorption. III

Abstract

The far wing line shape theory developed previously and applied to the calculation of the continuum absorption of pure water vapor is extended to foreign-broadened continua. Explicit results are given for H2O–N2 and H2O–CO2 in the frequency range from 0 to 10 000 cm−1. The theory is based on the quasistatic and binary collision approximations and assumes for the interaction potential an isotropic Lennard-Jones part and the leading anisotropic multipolar (dipole–quadrupole) term. For H2O–N2, the positive and negative resonant frequency average line shape functions and absorption coefficients are calculated for a number of temperatures between 296 and 430 K for comparison with existing laboratory data. In general, the agreement is very good, especially at the higher temperatures for which the experimental absorption is larger and the corresponding error limits are smaller. For H2O–CO2 for which no experimental data exists, the calculations are made only at 296 K. Because of the significantly different line shapes for self vs foreign broadening, the ratio of the corresponding continuum absorption coefficients varies widely as a function of the frequency. The implications of this for absorption in the Earth’s atmosphere are discussed briefly.