Rotational states ofH2, HD, andD2on graphite

Abstract

The rotational states of ${\mathrm{H}}_2$, HD, and ${\mathrm{D}}_2$ adsorbed on graphite in the √3 × √3 R30° commensurate phase, were calculated using a product wave function consisting of a rotational part, itself a product of single-molecule rotational wave functions, multiplied by a spatial part which describes the motion of the molecular center of mass. The single-molecule rotational term is written as an expansion in free-rotor basis functions. The spatial part is given by a self-consistent-phonon wave function determined in a previous calculation. The rotational ground state for each species is found to be a nearly pure J=0 state, and the lowest group of excited states, which are essentially J=1 states, are split with an energy separation of about 2.5–2.7 meV. These excited states are separated from the ground state by an average energy which is given approximately by BJ(J+1), where B is the rotational constant of the molecule. Thus the rotational states of hydrogen molecules adsorbed on graphite are, to a good approximation, slightly hindered three-dimensional rotor states.