Collisional Relaxation Times for Nitric Acid Vapor

Abstract

It has been shown previously1 that it is possible to obtain information on gas phase collisional relaxation rates from the amplitude rather than the phase of the signal coming from the microphone of an optoacoustic cell. In that earlier work,1 we proposed a detailed theory, based on a numerical solution of the heat diffusion equation, to relate the microphone signal amplitude to collisional relaxation time. The theory was verified using mechanically chopped single frequency infrared laser radiation at moderate power levels and at suitable wavelengths for absorption by nitric oxide, a diatomic gas with known spectroscopic and thermochemical properties.1 In the present paper, we apply the theory to experiments on dry nitric acid vapor, a polyatomic gas with nine vibrational modes.2