Accommodation Coefficients on Gas Covered Platinum

Abstract

Accommodation coefficients on a platinum wire have been computed for five monatomic and five diatomic gases from Pirani gauge measurements at room temperature, 18.9° to 30.5°C. Through careful control of experimental conditions it was possible to apply exact theoretical relations for the effects of radiation, wire conduction, and free molecule conduction upon the temperature distribution along the gauge wire. For each of the gases the accommodation coefficient increases with pressure up to about 0.1 mm and then remains constant throughout the pressure range in which complete free molecule conduction exists, indicating the absence of complete gas saturation of the wire surface at the lower pressures. There is no detectable temperature coefficient in the small interval in which measurements were made. At room temperature the mean accommodation coefficients on a completely gas covered platinum wire are: helium, 0.403±0.001; neon, 0.700±0.002; argon, 0.847±0.002; krypton, 0.844±0.002; xenon, 0.858±0.002; hydrogen, 0.312±0.001; deuterium, 0.393±0.001; nitrogen, 0.769±0.002; carbon monoxide, 0.772±0.002; oxygen, 0.782±0.002.