Measurements and calculations of self-broadening coefficients of lines belonging to the 2ν2, ν1, and ν3 bands of H216O

Abstract

Using Fourier transform spectra (resolution ≈ 0.005 cm−1), the self-broadening coefficients of 340 lines belonging to the 2ν2, ν1 and ν3 bands, and to the ν2 + ν3 − ν2 hot band of H216O, have been measured. The average uncertainty is about 19% and varies from 15 to 28% depending on the line involved. The broadening coefficients, by natural water vapor, of 40 other lines belonging to the ν3 and ν1 bands of H217O and H218O have also been measured. Theoretical calculations of self-broadening coefficients are performed, using the Anderson–Tsao–Curnutte method, and taking into account the four intermolecular interactions: dipole–dipole, dipole–quadrupole, quadrupole–dipole, and quadrupole–quadrupole. In these calculations, accurate spectroscopic data have been used: precise energy levels, realistic wavefunctions, and a complete dipole moment operator expansion in order to compute the transition probabilities. Particularly, all resonances between the three interacting vibrational states (020), (100), and (001) have been fully taken into account. For B-type bands, comparisons are made with the self-broadening coefficients previously calculated by Benedict and Kaplan for the pure rotational lines. The Anderson–Tsao–Curnutte method has proved to be very efficient for calculating self-broadening coefficients: the relative differences between observed and calculated values are less than 20% respectively for 68, 79, and 79% of the lines in the 2ν2, ν1, and ν3 bands. These self-broadening coefficients will be useful for the study of the absorption coefficient in line wings.