Direct Infrared Photodesorption of PhysisorbedH2

Blackbody radiation induced desorption rates of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ physisorbed on a Cu(510) surface were determined via electron-energy-loss measurements. Intense dipole-excited vibrational transitions to high-lying bound levels in the physisorption well indicate the possibility of direct infrared photodesorption. We have calculated rates for such a mechanism from spectroscopic data for ${\mathrm{H}}_2$ adsorbed on the (100)-like terraces and find excellent agreement with the experimental results.