Relaxation rates from time of flight analysis of molecular beams

Abstract

In the free jet generated when a gas is expanded from a reservoir at stagnation temperature T₀ and pressure P₀ into a vacuum chamber, substantial lags can occur in the conversion of internal energy into directed kinetic energy of the expansion. An analytical technique is presented for determining rotational energy relaxation rates from velocity distributions measured on the axis of the free jet at a fixed distance from the sonic throat. The agreement with rates obtained by other methods is good. Some sample experimental and analytical results for carbon dioxide, oxygen, hydrogen, and methane are presented.