Photoacoustic design problems in low pressure and cryo temperature operation

Microphone operation at low pressure and temperature is necessary in order to derive needed vibrational relaxation data for methane. Measurements were made using a specially designed photoacoustic cell. The successful low-pressure operation of the cell is borne out by theoretical computations. It is demonstrated that low-pressure vibrational lifetimes can be measured successfully in methane down to the cryo temperatures of interest to planetary atmospheric modelers. The photoacoustic technique appears capable of producing vibrational relaxation data over wide pressure range, wider than that often reported by fluorescence measurements