Experimental determination of the reaction time for hydrogen isotope exchange H2+D2→2HD on Ni(110)

Abstract

The mean reaction time of the hydrogen isotope exchange reaction H2+D2→2HD on the Ni(110) surface has been measured in a high-resolution time-of-flight (TOF) scattering experiment. The reactants were supplied by a pulsed supersonic D2 nozzle beam with incident energy Ei⩽120 meV and by a room temperature effusive H2 source. The TOF spectra of the product HD molecules measured with a chopper located between the incident D2 beam and the sample are a convolution of the reaction time τ on the surface and the velocity distribution of the desorbing HD products. The latter distribution is then measured with a chopper placed between the sample and the detector. The reaction time τ as determined from a deconvolution of the two spectra decreases with increasing surface temperature Ts from τ∼3000 μs at Ts=450 K to τ∼10 μs at Ts=700 K. An Arrhenius plot of the reaction time reveals that the reaction energy is Er=440 meV at surface temperatures below about Ts=600 K and Er=790 meV for temperatures Ts>700 K. Possible interpretations for the two reaction channels are proposed.