Contribution of electronically excited states to the radiation chemistry of organic systems. Progress report, September 1, 1976--August 31, 1977

The fluorescence of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) has been studied in the solvents n-hexane, methylcyclohexane, cyclohexane, isooctane, and tetramethylsilane for excitation energies below and above the photoionization threshold. Evidence is obtained for the existence, as a major intermediate in the photoionization process of a coherent but spatially diffuse excited state of TMPD. Electron impact spectra of NH3 at low energies and 900 scattering angle has failed to reveal any evidence for a low-lying valence triplet. For simple saturated hydrocarbons, large angle electron-impact spectra also fail to reveal any evidence for low-lying valence triplet states. Therefore if valence-shell transitions exist at all in these molecules they must be imbedded at significantly higher energies in the absorption manifold. The fluorescence of the A → X transition in ammonia-d3 has been studied in the presence of saturated hydrocarbon perturbers up to densities of approximately 6 M. Essentially no change in fluorescence quantum yield is observed. This eliminates inelastic processes as contributing importantly to pressure broadening and to shifting of the A reverse arrow X transition. The pressure broadening and pressure shifting of the first 10 vibrational peaks in the A reverse arrow X (n/sub N/ → 3s Rydberg) absorption of NH3 has been studied using He, Ne, Ar, N2, CH4, CF4 and SF6 gases up to pressures of approximately 100 atm. Both blue and red shifts are observed depending on the nature of the perturber. A dependence of the magnitude of the shift on vibrational level is observed and attributed to important variations of the electronic wavefunction of the upper state with position of the nuclei