The accommodation coefficient of helium on platinum has been measured at 77, 193, 273, and 373°K; and the values obtained at these temperatures for a clean platinum surface are 0.090, 0.043, 0.071, and 0.072 (±0.004), respectively. When the platinum is allowed to remain in contact with the helium for twenty-four hours or more, the accommodation coefficient values increase to 0.43, 0.071, 0.170, and 0.170 (in the same temperature order). Little adsorption occurs at 193°K, but strong van der Waals adsorption appears at 77°K and activated adsorption at the higher temperatures.

• Received 20 December 1943

DOI:https://doi.org/10.1103/PhysRev.65.185