SPECTRA AND PHOTOCHEMISTRY OF TRIFLUORONITROMETHANE ADSORBED ON ALKALI-HALIDE FILMS

The infrared spectrum of trifluoronitromethane (CF3NO2) physically ads orbed on sublimated alkali halide (NaCl, NaBr, KCl, and KBr) films in submonolayer and multilayer coverages, and isolated in argon and nitro gen matrices, has been observed. The fundamental vibrations exhibit so me surface-specific shifts, and there is indication that rotation abou t the CN bond is hindered upon adsorption. As in the gas phase, ultrav iolet irradiation of the adsorbed species leads to the production of a dsorbed carbonyl fluoride (CF2O), but an adsorbed FNO photoproduct was not observed, presumably lost to a secondary photolysis. Quantum effi ciencies for photolysis were determined for submonolayer and multilaye r species and were found to be independent of temperature (Phi = 0.20 +/- 0.20 adsorbed; 0.29 +/- 0.20 multilayer), reduced from that of the matrix-isolated species. These quantum efficiencies were used to dete rmine rate constants for surface-induced relaxation of the adsorbate a s a function of surface composition and temperature. Desorption isothe rms for bath CF3NO2 and CF2O were observed and fit to a first-order ki netic model of desorption, with activation energies of desorption of 1 4 +/- 5 kJ mol(-1) for CF3NO2 on the sodium salts, 16 +/- 5 kJ mol(-1) for CF3NO2 on the potassium salts, and 28 +/- 6 kJ mol(-1) for CF3NO2 desorbing from overlayers.