ADSORPTION AND INTERLAYER MIXING OF METHANE ON NI(100) AT 20 K

The adsorbed states of methane on Ni(100) at 20 R have been studied by IRAS and TPD. For the first layer CH4, bands are observed at 3000, 28 84 and 1298 cm(-1). On the other hand, only two bands are observed at 3017 and 1304 cm(-1) for the second layer CH4. The bands between 3000 and 3017 cm(-1) are assigned to the degenerate CH stretching mode (v(3 )), the bands between 1294 and 1304 cm(-1) to the degenerate deformati on mode (v(4)), and the 2884 cm(-1) band to the symmetric CH stretchin g mode (v(1)), respectively. Desorption temperatures of the first laye r and the second layer methane are similar to 51 and similar to 34 K, respectively. The observed enhanced sticking on the covered surface is due to efficient energy transfer to the adsorbate owing to mass match ing. In addition, interlayer mixing between the first layer and the se cond layer methane takes place during the adsorption process. The enha nced interlayer mixing observed for the post-dosing of Xe on the metha ne covered Ni(100) surface suggests that the adsorption energy of the incoming particle plays an important role in the interlayer mixing.