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Spectra and Photochemistry of Trifluoronitromethane Adsorbed on Alkali Halide Films

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Mariaelena Galie, Janine M. Rusnock, Michael E. Yevich, and Christopher A. Baumann*

Department of Chemistry, The University of Scranton, Scranton, Pennsylvania 18510-4626

J. Phys. Chem. B, 1997, 101 (41), pp 8304–8314

DOI: 10.1021/jp971995j

Publication Date (Web): October 9, 1997

Section:

Physical Organic Chemistry

Abstract

The infrared spectrum of trifluoronitromethane (CF₃NO₂) physically adsorbed on sublimated alkali halide (NaCl, NaBr, KCl, and KBr) films in submonolayer and multilayer coverages, and isolated in argon and nitrogen matrices, has been observed. The fundamental vibrations exhibit some surface-specific shifts, and there is indication that rotation about the CN bond is hindered upon adsorption. As in the gas phase, ultraviolet irradiation of the adsorbed species leads to the production of adsorbed carbonyl fluoride (CF₂O), but an adsorbed FNO photoproduct was not observed, presumably lost to a secondary photolysis. Quantum efficiencies for photolysis were determined for submonolayer and multilayer species and were found to be independent of temperature (Φ = 0.20 ± 0.20 adsorbed; 0.29 ± 0.20 multilayer), reduced from that of the matrix-isolated species. These quantum efficiencies were used to determine rate constants for surface-induced relaxation of the adsorbate as a function of surface composition and temperature. Desorption isotherms for both CF₃NO₂ and CF₂O were observed and fit to a first-order kinetic model of desorption, with activation energies of desorption of 14 ± 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.