Rotational excitation from a molecular mirror: NO scattering from Ru(0001)-(1 x 1)H

The rotational state distributions of NO molecules scattered off the (1 x 1)H-covered Ru(0001) surface have been investigated by resonance enhanced multi-photon ionisation (REMPI). Angular and energy distributions reported earlier for this scattering channel, show an angular spread of only ≃8° (θi = 60°, Ei = 2.1 eV), combined with small translational energy loss in the collision (Ef/Ei = 0.91). These observations suggest scattering from a very weakly corrugated surface, a 'molecular mirror', and a high probability to yield cold rotational distributions. The present experiments, however, reveal substantial rotational excitation, accompanied by rotational rainbows for higher quantum numbers (J > 20). The rotational temperatures increase from