Multichannel dissociation of physisorbed chlorobenzene by KrF laser radiation

The photochemistry in adsorbed molecules is drastically different from that of gaseous ones. Seven channels of KrF laser-induced dissociation of chlorobenzene condensed on silica have been found using mass spectrometry. They include the multiple photon detachment of H and Cl atoms and the opening of the aromatic ring. A general approach is proposed for adlayer photolysis based on the excitation of molecules into repulsive electronic states when bonds are stretched. It consists of the multiphoton transition of molecules into high vibrational levels in the vibronic continuum, bond elongation, and stimulated photoemission. Secondary processes in desorbed fragments were also studied.