Abstract

Theoretical absorption spectra for nitric acid in the 11.3 micron spectral region were generated by line by line integration. Only the v₅ and 2v₉ bands were considered. The rotational line positions and intensities were calculated using Dana's constants for the v₅ band; for the 2v₉ band the rotational constants were based on the results given by Chevillard and Giraudet² in conjunction with an ab initio calculation using the vibrational constants of McGraw et al³. A Lorentzian line shape was used with a self broadened semi-­half width of 0.75 cm^-1 at 300K and 1 atm. The semi-half width was assumed constant and at this stage of the work the varia­tion with rotational quantum number was ignored. Fig. 1 shows a comparison between a calculated spectra and an experimental spectrum of Goldman et al⁴. The differences between the calcu­lations and the experimental results could be due to the following; (a) neglect of a large number of the weaker lines, it was necessary to eliminate a number of weaker lines for computational purposes; (b) neglect of possible hot bands, as will be noted below there could be hot bands in the vicinity of 885 cm⁻¹ and 910 cm⁻¹; (c) the possibility that the wings of the lines are super Lorentzian.

© 1980 Optical Society of America