The 21.8 µm absorption bands of HNO3 vapor were measured at 40°C. Statistical-band-model analysis of the data resulted in spectral-band-model parameters and yielded an integrated intensity of 393 ± 15% (cm-2 atm-1) at 40°C between 390 and 502 cm-1.
A. Goldman, F. S. Bonomo, W. J. Williams, and D. G. Murcray, "Statistical-band-model analysis and integrated intensity for the 21.8 µm bands of HNO3 vapor," J. Opt. Soc. Am. 65, 10-12 (1975)