Robert M. Reese

Mass‐Spectrometric Study of Photoionization. III. Methane and Methane‐d4

Photoionization‐efficiency curves for the molecule and fragment ions of CH4 and CD4 are obtained in the wavelength region 1000 to 600 A. The electronic structure of the molecule ion is related qualitatively to the shape of the parent‐ionization‐efficiency curve and the implications of the complicated vibronic behavior of the CH4+ ion are discussed. A qualitative explanation is given for the observed isotope effect on the parent‐ionization‐efficiency curve and on the fragment‐ion threshold energies. New upper bounds for the ionization energies I(CH4) = 12.71 eV and I(CD4) = 12.87 eV are obtained. Other thermochemical values deduced from the study are: D(CH3–H) = 4.41 eV, D(CD3−D) = 4.55 eV, D(CH2–H) = 4.87 eV, and ΔHf (CH2) = 4.07 eV. Zero‐point differences for methyl and methylene ions and neutrals are also estimated.

Electron Impact Studies of Sulfur Dioxide and Sulfuryl Fluoride

Mass spectra and appearance potentials have been obtained for the principle positive and negative ions of SO2 and SO2F2. Ionic heats of formation and probable ionization‐dissociation procesess are tabulated. The electron‐impact data for SO2 support the values of 3.3 ev for D(S2) and 5.15 ev for D(SO). The molecular ionization potential is in good agreement with recent photoionization measurements. The ΔHf(SO2F2) = — 205 kcal/M is calculated from the appearance potential of the SO2+ ion. Other ionic heats of formation are based on this value. The ΔHf(SO+) is in good agreement for both molecules. A minimum value of 3.0 ev is calculated for the electron affinity of F2 from the appearance potential of the F2‐ ion.

Mass spectrometric study of photoionization. I. Apparatus and initial observations on acetylene, acetylene-d2, benzene, and benzene-d6

A windowless vacuum ultraviolet monochromator and mass spectrometer are combined for the study of photoionization processes in the energy range 2000 to 600 A (6 to 21 eV). Details of the apparatus and techniques of operation are given and results are reported for an initial study of acetylene, acetylene-d2, benzene, and benzene-d6. Ionization energies of 11.406 and 11.416 eV are obtained for the 1πu electron of C2H2 and C2D2, respectively. Vibrational levels of the ground state of the ion are observed with quantum intervals of 1855 cm−1(C2H2) and 1775 cm−1(C2D2). Ionization energies for the e1g(π) electron of C6H6 and C6D6 are determined to be 9.242 and 9.245 eV, respectively. Quantum intervals for vibrational levels of the ground state ions are apparently equal for the two isotopic molecules and estimated to be 800 cm−1. A second onset of ionization is observed at 11.53 eV for C6H6 and at 11.59 eV for C6D6. Results agree well with spectroscopic data.

Mass‐Spectrometric Study of Photoionization. II. H2, HD, and D2

Mass‐spectrometric techniques have been used to obtain the photoionization‐efficiency curves for H2, HD, and D2 in the energy range 815 to 700 A (15.2 to 17.7 eV). A qualitative description of the observed autoionization process, based on a theory proposed by Fano, is applied to an analysis of the results.

Photoionization Mass Spectrometry of NO

The photoionization efficiency curve of the NO molecule has been measured in the range 1360–600 A, and the autoionization structure compared with the absorption spectrum. A number of plausible vibrational progressions are suggested in the 1130–900 A range.

Some Ions of High Kinetic Energy in Mass Spectra of Polyatomic Molecules

When the lighter‐fragment ions of hydrocarbons and hydrocarbon derivatives are recorded with low‐ion accelerating voltages, one observes satellite peaks on the high‐mass side of the main peaks that come from ions with a fairly homogeneous high kinetic energy. Observations of the satellite peaks of CH3+ ions in mass spectra of 13 hydrocarbons and CH3CF3, are reported. The kinetic energies range from 1.5 to 3.4 ev and the relative intensities have a wide range of values but are less than the main peak except in benzene. The appearance potential of the satellite peak is roughly 30 volts in most cases while the main peak is observed above 20 volts. These high‐energy ions are ascribed to doubly charged molecule ions that dissociate into two singly charged fragments. The kinetic energy of the pair of fragment ions is in most cases nearly equal to the Coulomb energy of two ions at a distance equal to the greatest distance between valence electrons in the molecule.

Ionization and Dissociation of Nitrogen Trifluoride by Electron Impact

A mass spectrometric study of nitrogen trifluoride provides data on the relative abundances and appearance potentials of the NF3+, NF2+, NF+, N+, F+, F—, and F2— ions. The heat of formation of the NF3 molecule is used to determine the probable processes of formation of the N+ and F+ ions and to calculate the ionization potentials of the NF and NF2 radicals.

Ionization and Dissociation of Perchlorylfluoride by Electron Impact

Relative abundances and appearance potentials are reported for both positive and negative ions observed in the mass spectrum of perchlorylfluoride. Appearance potentials of the atom ions result in a value for ΔHf(ClO3F) of nearly zero within the experimental uncertainty. Bond dissociation energies and ionization potentials of the chloryl radicals are estimated from appearance potentials of the polyatomic ions. The energetics of probable ionization‐dissociation processes are compared with observed data.

Ionization and Dissociation of Hexafluorobenzene by Electron Impact

Mass spectra and appearance potentials are presented for the principal positive and negative ions of hexafluorobenzene along with comparative data for benzene. Although complete analysis of bond dissociation energies is prevented by lack of thermochemical data, the C–F bond is estimated to be 145 kcal. Qualitatively, the results indicate that C6F6 is thermally more stable than C6H6 and is a relatively stable configuration in the presence of ionizing radiation.

Ionization and Dissociation of Oxygen Difluoride by Electron Impact

The mass spectrum of OF2 includes the ions OF2+, OF+, O+, and F—. The ionization potential of the molecule and appearance potentials and excess kinetic energy are measured for the OF+ and F— ions. The known heat of formation of OF2 and the appearance potential of the F— ion permit calculation of the bond dissociation energies D(FO–F) and D(O–F) and an estimate of the ionization potential, I(OF). Dissociation energies estimated for the OF2+ ion are consistent with those of the neutral molecule.