INELASTIC NEUTRON-SCATTERING FROM H-2 ON VAPOR-DEPOSITED CO2

Inelastic neutron scattering spectra at 17 meV and 68 meV incident ene rgies of molecular hydrogen adsorbed on vapour deposited substrates of pure CO2, 90:10 and 50:50 CO2:Kr are reported. The ortho-para transit ion is shifted from 14.7 meV in the free H-2-molecule to 9.4 meV in a presumably commensurate ortho-H-2 monolayer on the CO2 surface. The qu adrupole-quadrupole interaction of ortho-H-2 molecules with the CO2 su bstrate results in a strongly anisotropic potential. In addition to ro tations the dynamics of this layer comprise a local Einstein mode and phonons in resonance with the substrate, giving rise to intense multip honon transitions. Quasielastic scattering on warmer samples is assign ed to a liquidlike adsorption layer, in which the H-2 rotations are st rongly perturbed.