Melting of a p-H2 monolayer on a lithium substrate

Adsorption of para-hydrogen films on Alkali metals substrates at low temperature is studied theoretically by means of Path Integral Monte Carlo simulations. Realistic potentials are utilized to model the interaction between two para-hydrogen molecules, as well as between a para-hydrogenmolecule and the substrate, assumed smooth. Results show that adsorption of para-hydrogen on a Lithium substrate, the most attractive among the Alkali, occurs through completion of successive solid adlayers. Each layer has a two-dimensional density approximatley equal 0.070 inverse square Angstroms. A solid para-hydrogen monolayer displays a higher degree of confinement, in the direction perpendicular to the substrate, than a monolayer Helium film, and has a melting temperature of about 6.5 K. The other Alkali substrates are not attractive enough to be wetted by molecular hydrogen at low temperature. No evidence of a possible superfluid phase of para-hydrogen is seen in these systems.