The Measurement of Energy Transfer in Gas-Solid Surface Interactions Using Electron Beam Excited Emission of Light

摘要

A new approach is described to the measurement of energy accommodation of a rarefied gas at a solid surface. Gas molecules from a surrounding gas in thermal equilibrium and at rest are incident on a cooled metal target disc. Under conditions of free-molecule-flow the incident molecules are not disturbed by the cooler reflected molecules. A high energy electron beam is passed through the gas in front of the target disc and parallel to it, exciting the gas to electroluminescence. The rotational energy distribution and number density of molecules can be determined from a spectrographic analysis of the light emitted by the gas. The contribution to the measured intensity of spectrum lines due to the incident molecules can be determined with the target retracted, and then subtracted from total light intensity measurements made with the target in position in order to get the rotational energy distribution and number density of the reflected molecules alone. Measurements made with nitrogen on a silver target showed that the translational and rotational degrees of freedom both had an accommodation coefficient alpha = 0.85, and that the rotational energy distribution of the reflected molecules corresponded to that of gas in thermal equilibrium.