Desorption by electronically stimulated adsorbate rotation

Time-of-flight laser resonance ionization is used to measure state-selective translational energies of neutral NO, CO, and metastable CO (${\mathrm{a}}^3$Π) desorbed from Pt(111) upon electron impact. A novel and dominant NO channel has a threshold of ∼6 eV and a peak translational energy of 0.05 eV. Lifetime calculations reveal a long-lived simple excitation (5${\mathrm{\sigma }}^{\mathrm{-}1}$). Dynamical calculations reproduce translational and rotational energy distributions and suggest that the excitation frees the hindered rotation of NO.