Temperature rises produced by a molecular beam striking a platinum surface

Abstract

A platinum surface initially at room temperature is exposed to intense molecular beams of He, Ar, H{sub 2}, N{sub 2}, and SF{sub 6} emerging from a nozzle also at room temperature. The mass of the platinum is small, so after a few minutes it reaches a steady temperature uniform throughout the sample. Because the rate of heat loss to the surroundings is low, a thermocouple records temperature rises that for pure gases are as much as 30 K and that for mixtures of He with Ar can exceed 100 K. Interpretation of the results shows that these rises can be understood quantitatively and thus provide information about energy transfer occurring when gaseous molecules collide with surfaces. In particular the method gives (1) a way of measuring the temperature T{sub s} a surface attains at steady state due to interaction with gas molecules in the absence of heat conduction or radiation, (2) a simple determination of the average kinetic energy E{sub i} = 2k{sub B}T{sub s} of an incoming atomic beam without the need for measurement of the velocity distribution or the flux in the beam, and (3) a quantity {gamma} that, like an energy accommodation coefficient, is a measure ofmore » the effect of the temperature of the surface on the scattering.« less