Fizika Nizkikh Temperatur: Volume 27, Number 9-10 (September 2001), p. 1138-1147    ( to contents , go back )

Isotope effects and effect of 2D phase transitions in the kinetics of low-temperature (down to 5 K) hydrogen adsorption

V. D. Osovskii, Yu. G. Ptushinskii, V. G. Sukretnyi, and B. A. Chuikov

Institute Physics National Academy of Sciences Ukraine, av. Nauki 46, Kiev, 03028, Ukraine
E-mail: ptush@iop.kiev.ua
pos Анотація:

Received April 2, 2001

Abstract

The adsorption-desorption characteristics of hydrogen isotopes on the (110) W and Mo surfaces are studied at Ts ~ 5 K. It is found that the characteristics for hydrogen and deuterium differ essentially from each other. Isothermal desorption of H2 from W(110) is observed at Ts ~ 5 K, but there is no observable desorption of D2 . H2 desorption is strongly suppressed by increasing the molecule flux emerged to the surface. In the authors` opinion, this is due to the 2D gas ≈ 2D condesate phase transition. The initial sticking probability S0 of H2 significantly depends on molecule flux, whereas S0 of D2 does not depend on it. The nucleation of the 2D condensed phase during the molecules` life time in the precursor state is supposed to be the reason for the S0 growth. A sharp and deep minimum in the coverage dependence of the sticking probability is observed in the case of H2 adsorption on Mo(110). Such a peculiarity does not exist in the case of D2 adsorption. The above isotope effects are supposed to be due to the deeper position of the zero-point vibrational level of heavier D2 molecules.

PACS:
68.45.Da -
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