Non-thermal photodesorption of N2 from Ag (111)

We have measured translational and rotational energy distributions of N-2 molecules following desorption from a Ag(lll) surface by infrared (1064 nm) radiation. The observed desorption yields were large even at laser fluences far below that required for laser-induced thermal desorption. State-resolved laser techniques using coherent VUV radiation showed that the rotational and translational energy distributions of the desorbing N-2 molecules are not consistent with the predictions of the heat diffusion model governing laser-induced surface heating. These results suggest that physisorbed adsorbates can couple directly to the nascent-phonon distribution or the nascent electron-hole pairs in the photoexcited substrate without heating of the surface.