Negative ion Morse potential energy curves for cytosine (C) and thymine (T) consolidate electron affinity, gas-phase acidity, bond dissociation energy, photoelectron spectrum, electron impact, transmission, and transfer data. We have previously published experimental adiabatic electron affinities for guanine, 1.51 ± 0.05; adenine, 0.95 ± 0.05; C, 0.56 ± 0.05; uracil, 0.80 ± 0.05; and T, 0.79 ± 0.05 (all in eV). These values were obtained from half-wave reduction potentials in aprotic solvents and verified by AM1 semiempirical multiconfiguration configuration interaction (AM1-MCCI) calculations. We present a computer simulation of thermal charge-transfer experiments to support these values. Unpublished negative chemical ionization mass spectrometry data support our gas-phase acidities:  for A, G, and T, 14.1; for U, 14.2; and for C, 14.3 (all in eV). We use dipole-bound and valence-state electron affinities previously obtained from photoelectron spectra (Schiedt, J.; Weinkauf, R.; Neumark, D. M.; Schlag, E. W. Chem. Phys. 1998, 239, 511). We interpret monoenergetic electron beam spectra reported in the literature to obtain vertical electron affinities, negative ion distributions, and limits to bond dissociation energies for C and T (Huels, M. A.; Hahndorf, I.; Illenberger, E.; Sanche, L. J. Chem. Phys. 1998, 108, 1309).

Adiabatic absolute electron affinities (EA) of about 80 aromatic hydrocarbons are calculated from literature values of half wave reduction potentials in aprotic solvents. Solution energy differences are estimated by grouping the molecules based on experimental and theoretical values, chemical logic and statistical analysis. The electronegativity values, (IP+EA)/2, calculated using literature data for ionization potentials, are constant for many of the compounds. Others vary in a systematic manner, such as benzene, 4.26±0.05; naphthalene, 4.14±0.02; anthracene, 4.06±0.02; tetracene, 4.03±0.03; pentacene, 3.98±0.03, in eV. Theoretical values, recalculated from the beginning, compare favorably with the literature values. Three independent methods for obtaining absolute EA’s are summarized and verified; the calibration of reduction potentials, the combination of ionization potentials with electronegativities and the use of semiempirical methods.

The reaction of SF6 with thermal electrons has been studied in a Ni-63 atmospheric pressure ionization source for a quadrupole mass spectrometer (API/MS). The major ions that are observed are the parent negative ion (SF−6) and the parent minus a fluorine atom (SF−5). The ratio of [SF−5]/[SF−6] is highly temperature dependent above 500 K. The dissociation energy of the ground state negative ion into SF−5 and F has been determined to be 1.35±0.1 eV. This gives values of 3.8±0.15 eV for the electron affinity of SF5 and 1.15±0.15 eV for the electron affinity of SF6. The negative ion states of sulfur hexafluoride have been described by ‘‘pseudo-two-dimensional’’ Morse potentials calculated using experimental data.

is no experimental evidence for isomers of other size clusters. Fourth, it could be that significant differences in such properties as hydrogen desorption energy, and metal hydride or metal carbide bond strengths, may account for the different product distributions, as a function of both size and metal type. In regard to the latter (27) Elkind,

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