A new method has been developed for the determination of translational thermal accommodation coefficients, αt, of vapors interacting with solid surfaces and has been used to measure αt for bromine, iodine, benzene, naphthalene, n-hexane, and ethylacetate on Pyrex glass in the temperature region 195 ° to 465 °K. The values obtained (0.55, 0.64, 0.37, 0.37, 0.47, and 0.46, respectively) have a probable accuracy of ±0.06 or better and are only slightly temperature-dependent.
The method, which can be easily adapted for the study of interactions with surfaces other than glass, requires the measurement of the mean velocity of molecules leaving the solid surface. This is accomplished by passing a selected beam of the molecules through the sensitive volume of an ion gauge. The only restriction on the method is that the pressure of the vapor at the temperature of the wall of the gauge should be very low (e.g., 10−12 Torr).