ADSORPTION OF H2 AND D2 ON W(111) AND W(110) SURFACES AT LOW-TEMPERATURES (DOWN TO 5-K)

Using thermal desorption mass-spectroscopy and molecular beam measurements we have revealed weakly bound molecular-adsorption states of H-2 (D2) on the W(111) and W(110) surfaces with T(des) almost-equal-to 5 and 8 K as well as on W(110) with T(des) = 60 K. Several dissociative adsorption states of H-2 (D2) are observed in agreement with earlier studies. The dissociative adsorption of H-2 (D2) is shown to take place at T(ad) almost-equal-to 5 K. The simultaneous filling of both molecular and atomic states on the W(110) surface, occurring even at zero coverages, evidences an existence of two adsorption channels with significantly different activation barriers for dissociative adsorption.