A NEW MECHANISM FOR ABSORPTION - COLLISION-INDUCED ABSORPTION

The absorption of atomic hydrogen on Ni(111) is observed to be induced by collisions with Ar, Kr or Xe atoms incident with energies in the normal direction greater than 60 kcal mol-1. The mechanism for collision-induced absorption involves momentary deformation of the lattice which opens channels leading to the bulk metal into which the hydrogen diffuses. The embedded hydrogen is detectable by high-resolution electron energy loss spectroscopy and is distinguishable from the vibrational modes of chemisorbed hydrogen on the basis of the dependence of the inelastically scattered electron intensity on electron impact energy. The embedded hydrogen has a vibrational frequency of 800-850 cm-1 and is observed to recombine and desorb as H-2 between 180 and 220 K. Hydrogen absorption can also be achieved by exposure to atomic hydrogen. As much as an equivalent of 8 monolayers (ML) of hydrogen has been absorbed.