Survival of HCl(v=2) in trapping-desorption from MgO(100)

An HCl molecular beam incident on MgO(100) is photoexcited to v=2, J=1 by using a pulsed parametric oscillator. At a translational energy of 0.11 eV, incident HCl is adsorbed. Thermal desorption yields v=2 molecules whose rotational and translational degrees of freedom are equilibrated at the surface temperature. Surface residence times for v=2 might be as long as 1 μs. At 180 K, it is concluded that a large fraction of surface-bound v=2 molecules reenter the gas phase, while at 120 K, deactivation exceeds desorption by an order of magnitude. Deactivation probably takes place at steps.