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NH2 and NH transitions were identified in dispersed fluorescence spectra obtained by VUV excitation of NH3 at nine different energies between 8.266 and 15.498 eV. Fluorescence excitation (FEX) spectra between 6 and 15 eV were measured at seven specific emission wavelengths for these species. This extends the usual 11.7 eV upper limit of NH3 FEX spectra. Among the results of our work are the following: (i) a clarification of the assignment of the emission carriers; (ii) analysis of the FEX spectra of NH2(A 2A1 → 2B1) emission and assignment of the features to members of the npe′ ← 1a″2, nde″ ← 1a″2, nsa′1 ← 1a″2 and nda′1 ← 1a″2 Rydberg series transitions of NH3; (iii) new information on photodissociation processes leading to formation of NH2(A 2A1) and of NH in various excited states, in particular concerning the formation of NH (A 3Π) at 8.266 eV by dissociation of the a 3A″2 state of NH3, the existence of a potential barrier of 360 ± 70 meV in the dissociation to form NH (c 1Π) at 9.85 eV and its formation from a non-planar state above 11.3 eV; (iv) information pertaining to the heat of formation of the NH radical, which we determine as ΔHf,0°(NH) = 3.70 ± 0.01 eV, and to the thermochemical limits of the dissociation reactions of NH3.

Deuterium isotope effects on the photofragmentation thresholds of naphthalene monocations are studied by photoion mass spectrometry using variable-energy monochromatized synchrotron radiation to photoionize C 10 H 8 and C 10 D 8 . Kinetic isotope shifts (d-h) in the range 30-780 meV were observed for seven fragmentation reactions in the 15-20-eV region. The physicochemical factors leading to kinetic isotope effects are discussed. The observed kinetic isotope shifts are rationalized, mainly in terms of the RRKM/QET model and the specific reaction mechanism pathways

Deuterium isotope effects on the photofragmentation thresholds of naphthalene monocations are studied by photoion mass spectrometry using variable-energy monochromatized synchrotron radiation to photoionize C 10 H 8 and C 10 D 8 . Kinetic isotope shifts (d-h) in the range 30-780 meV were observed for seven fragmentation reactions in the 15-20-eV region. The physicochemical factors leading to kinetic isotope effects are discussed. The observed kinetic isotope shifts are rationalized, mainly in terms of the RRKM/QET model and the specific reaction mechanism pathways

Hydrogen-bonded clusters of methyl, ethyl-, dimethyl-, and diethylamines are synthesized in a seeded supersonic expansion for a mass spectroscopic study. The mass spectra are compared by ionizing either with 21-eV electrons or with photons from dispersed synchrotron radiation. Photoionization efficiency curves are measured to determine threshold energies for the ionization and fragmentation of the clusters. The threshold values yield gas-phase proton affinities, association, and dissociation energies by thermochemical calculations. The derived thermochemical quantities of cluster ions depend on the amount of the association energies of the neutral clusters. The association energy data found in this study are compared with previously calculated values. Lower bounds to the bond dissociation energies of alkylamine cluster ions are presented. The absolute proton affinity values of CH/sub 3/NH/sub 2/ (930 +/- 15 kJ/mol), C/sub 2/H/sub 5/NH/sub 2/ (940 +/- 15 kJ/mol), (CH/sub 3/)/sub 2/NH (955 +/- 15 kJ/mol), and (C/sub 2/H/sub 5/)/sub 2/NH (965 +/- 15 kJ/mol) determined in this study are about 30 kJ/mol higher than the currently recommended reference data. The proton affinities of molecular aggregates are determined in order to quantify the first steps of gas-phase proton solvation energetics.