Analysis of neutral fragments from ultraviolet laser irradiation of a photolabile triazeno polymer

A photolabile triazeno polymer was irradiated with pulsed excimer laser lig ht at 248 nm and 30 ns pulse width. The ablation fragments were analyzed us ing time-of-flight (TOF) mass spectrometry. At fluences below 1.3 J/cm(2), only neutral products were found. At these fluences, N-2 is by far the most intense neutral signal along with measurable phenyl radical (mass 76) prod uction. The N-2 TOF shows a fast shoulder corresponding to kinetic energies of about 1.1 eV and a long slow tail persisting for hundreds of microsecon ds. The tail is attributed to delayed emission of reaction products from th e polymer. The kinetic energy of the fast peak is attributed to direct ejec tion of products from surface sites undergoing exothermic decomposition. A weaker signal due to the phenyl radical is also observed. The observed flue nce dependence of the two major products is highly nonlinear and is shown t o fit an Arrhenius equation. We discuss the implications of these measureme nts regarding photochemical versus photothermal processes. (C) 1999 America n Institute of Physics. [S0021-8979(99)07924-4].