Kinetic Studies Using a Highly Sensitive Microphone Detector

A very sensitive microphone detector is used to study fast kinetic rate processes in the gas phase resulting in the generation of heat. The rate of heat evolution in turn produces a short duration pressure pulse which drives the microphone. The frequency response of the microphone is somewhat slower than required to record these pulses as they actually appear at the detector. The theory of the method used for the data reduction is presented. It is based upon the Green’s Function method which expresses the time dependent microphone signal, X, (t), as the convolution of the pressure pulse function, f(t), by the microphone’s impulse response function, G(t). A Fourier analysis of X(t) and the two relevant functions, f(t) and G(t), at a single frequency, allows direct determination of the rate constant for the kinetic process under study. The method is demonstrated by applying it to the study of vibrational energy relaxation of pentafluorobenzene in argon buffer gas and gives results in agreement with other experimental methods.