Photon stimulated desorption of neutral hydrogen atoms from condensed water and ammonia by resonant Ols and Nls excitation: search for the signature of ultrafast bond breaking

A highly sensitive detector for neutral particles has been designed and app lied to photon stimulated desorption from condensed NH3, and adsorbed and c ondensed H2O. Results on repulsive N1s and O1s core-to-bound excitations ar e reported, which for the isolated molecules are expected to stimulate ultr afast bond breaking and predominant emission of neutral H atoms. For NH3 an d H2O molecules on surfaces, strong H-atom signals are obtained for the ent ire O1s and N1s excitation energy range, but no selective enhancement due t o ultrafast dissociation, although the previously observed enhancement of H + emission is well reproduced. Possible matrix effects are discussed as an explanation for this contrasting behavior of isolated and adsorbed/condense d molecules. (C) 2000 Elsevier Science B.V. All rights reserved.