Deconvolution problems in a pulsed photoacoustic measurement of methane vibrational lifetimes at 77 K, 0.01 Torr

Abstract

A conventional gas phase photoacoustic measurement has proved to be less than straightforward due to difficulties associated with deconvolution of the microphone (Bruel and Kjær) response from the vibrational quenching lifetimes measured for methane in various binary buffer gases. The application of the lifetime data is to the aeronomy of Jupiter and preliminary results have been reported [Halthore et al., “Implications of the methane relaxation time measurements for the atmospheres of outer planets and Titan,” 21st Ann. Mtg. Div. Planetary Sci., AAS, 1989]. However, when extensive, accurate recordings were obtained this summer, a systematic error was noted that was attributed to convolution of the microphone's impulse response into the molecular relaxation dynamics. For this reason, it is felt that cw chopped laser excitation would be superior to the Nd‐YAG pulsed laser excitation presently used to pump the asymmetric stretch mode of methane at 3.3 μm. [Work supported by the Institute for Space and Terrestrial Physics, Space Astrophysics Laboratory, Toronto.]