The equilibration of the vibrational degree of freedom of hydrogen chloride was studied at pressures below 3 cm of mercury. The gas was excited to emission in a pulsed, microwave discharge. The light was dispersed by a monochromator and its intensity measured as a function of time for all resolved vibration-rotation lines in the region of the HCl fundamental. These measurements give a direct measure of the population density of the excited gas. All evidence points to the fact that equilibrium is established quickly between the translational and rotational degrees of freedom relative to the vibrations. Hence the measurements give the rate at which vibrational equilibrium is reestablished after the pulse. The observed dependence upon pressure is opposite to what one would expect from a collisional deactivation theory. The behavior was related to a diffusion process in which vibrational deactivation occurs primarily at the walls of the discharge vessel. Author
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