Albert C. Parr

Photoelectron–photoion coincidence study of the bromobenzene ion

The technique of variable time photoelectron–photoion coincidence mass spectrometry has been applied to the fragmentation of bromobenzene ion producing a phenyl ion. A detailed analysis of the variation of the breakdown curve with parent ion residence time was performed. The results lead to ΔH °f0 (phenyl ion)=270 kcal/mole in close agreement with recalculated results from an earlier study on chlorobenzene. This, combined with other photoionization results leads to ΔH °f0 (phenyl radical)=83±3 kcal/mole, slightly higher than the value 80.9±2 kcal/mole obtained from neutral kinetics. The analysis leads to a rate‐energy dependence for the fragmentation process and an equivalent 1000 K Arrhenius pre‐exponential factor of ∼9.4×1014 sec−1, which may be compared to the value 2×1015 sec−1 for the analogous neutral process. The possible contribution of spin orbit splitting is discussed.

Photoionization and threshold photoelectron—photoion coincidence study of propyne from onset to 20 eV

Abstract The photoionization efficiency curves for allene and its fragments C3H3+, C3H2+ and C3H+ are given from threshold to 20 eV. The threshold photoelectron spectra and breakdown curves are given over the same energy span. The adiabatic ionization potential is determined to be 9.69 ±0.01 eV and the heats of formation of the fragments are derived from the appearance potentials. Autoionization is found to be an important factor in the parent ionization and fragmentation.

Wavelength and vibrational‐state dependence of photoelectron angular distributions. Resonance effects in 5 σ photoionization of CO

Photoelectron angular distribution were studied for the photoionization of CO for v=0−3 in the range 16–26 eV. (AIP)

An angle resolved photoelectron spectrometer for atoms and molecules

Abstract An angle resolved photoelectron spectrometer has been constructed and coupled to the high throughout 2 m normal incidence monochromator now in operation at SURF-II. The electron analyzer whose design has been previously reported [2] scans the angular distribution of the ejected photoelectrons in a plane perpendicular to the partially polarized exit beam from the monochromator. The intensity of the photon beam from the monochromator is monitored by measuring the photocurrent from a screen in front of a three mirror polarization analyzer which is used to determine the degree of polarization of the photon beam. The function of the spectrometer is under computer control which is also acquires and processes the data output from the apparatus. Two novel features are employed to make the system highly effective: one is a capillary which channels the monochromatized output photon beam to the gas-photon-interaction zone and isolates the 10 −4 vacuum int the spectrometer chamber from the 10 −9 vacuum in the monochromator; the second feature is a high speed cryopump which permits a high density gas jet to interact with the photon beam while maintaining a high enough vacuum to minimize electron scattering and permit operation of the channeltron electron detector. These features combined with output fluxes of 5 × 10 10 photons/s −1 A −1 permit vibrationally resolved photoelectron spectra of N 2 and CO to be obtained in about 15 min.

Field ionization energy spectra of molecules

Abstract Considerations for determination of the partition of internal energy in ion s formed by field ionization are discussed in terms of the distribution of ion energies. Experimental high-resolution energy spectra for the molecular ions produced by field ionization of toluene, cycloheptatriene, phenol, hydrogen and carbon monoxide are shown and discussed. In particular it is concluded that the range of internal energies can be of the order of several electron volts. Implications of the observations for rate predictions are discussed.

The photoionization of allyl chloride from onset to 20 eV

Abstract Photoionization efficiency data have been obtained for the parent ion and two fragment ions (C 3 H 5 + and C 3 H 3 + ) of allyl chloride. Onset energies are determined for these ions and heats of formation calculated for the fragment ions. The structures of the fragment ions are discussed in relation to their heats of formation.