The importance of the plume ejection time for the fragmentation yields observed in the UV ablation of molecular van der Waals films. Ablation of chlorobenzene films at 248 nm

The efficiency of photolysis in the ablation of thick C6H5Cl films at 248 nm is probed over 40-300 mJ/cm(2) by means of time-of-flight quadrupole mass spectrometry. Up to approximate to 150 mJ/cm(2), the photolysis yield is considerably smaller than that in the gas-phase. We argue that because of plume ejection well after the laser pulse, photolysis occurs exclusively in the film, and as a result, permanent dissociation is limited by the operation of efficient recombination processes characteristic of condensed phases. Fragmentation starts being important only at higher fluences, at which desorption during the laser pulse is indicated to be significant.