S. H. Southworth

Vibrationally resolved photoelectron studies of the 7σ−1 channel in N2O

We present vibrationally resolved photoelectron studies of the 000, 100, 200, and 001 modes of the A state (7σ−1) of N2 O+ in the 17.4–26 eV photon‐energy range. The vibrational branching ratios σ(100)/σ(000) and σ(001)/σ(000) agree very well with fluorescence measurements by Kelly et al. and qualitatively with recent theoretical predictions of Braunstein and McKoy. The large non‐Franck–Condon variations in the σ(100)/σ(000) and σ(200)/σ(000) branching ratios are associated with a predicted 7σ→eσ shape resonance near 20 eV. Overall, the vibrational branching ratios imply lower resonant energies for the stretching modes (100 and 200) and a similar resonant energy for the asymmetric stretch (001), compared with the 000 mode. The vibrational asymmetry parameters (β) display a strong variation with energy which is qualitatively reproduced by theory; however, the experimental values for β(100) and β(001) exhibit additional structure around 20 eV. When combined with theory and recent fluorescence data, these r...

Vibronic coupling and other many‐body effects in the 4σ−1g photoionization channel of CO2

Vibrational branching ratios and photoelectron angular distributions were measured for 4σ−1g photoionization of CO2 in the energy range 20–28 eV. Of particular interest are three vibrational components of the resulting CO+2 C 2Σ+g state—the allowed (000) and (100) bands and the forbidden (101) band. The wavelength dependence of the beta parameter for the forbidden band deviated significantly from that of the two allowed bands, showing instead a strong resemblance to that of the B 2Σ+u state. This behavior suggests that vibronic coupling to the B 2Σ+u state is responsible for the appearance of the forbidden (101) band in the C 2Σ+g state photoelectron spectrum. We also observe evidence for other many‐body effects—shape‐resonance‐induced continuum–continuum coupling and doubly excited autoionizing resonances—in the present data.

Autoionization dynamics in the valence‐shell photoionization spectrum of CO

Autoionizing Rydberg series in the valence‐shell spectrum of CO have been studied by determining the high resolution relative photoionization cross section of cooled CO in the energy region 14.0–20.0 eV and by determining the vibrational branching ratios and the photoelectron angular distributions for production of CO+ X 2Σ+, v+=0–2 in the energy region 16.75–18.75 eV. Of particular interest are three prominent spectral features between 17.0 and 17.5 eV that result from interactions involving Rydberg series converging to the excited A 2Π and B 2Σ+ states of the ion. The results are discussed in the context of recent two‐step multichannel quantum defect theory calculations by Leyh and Raseev (the following paper).

Photoelectron spectrometer for high resolution angular resolved studies

Abstract We report on a new electron spectrometer system designed for use on storage ring light sources. The system features a large (76 cm diameter ×92 cm long) triply magnetically shielded vacuum chamber and two 10.2 cm mean radius hemispherical electron energy analyzers. One of the analyzers is fixed and the other is rotatable through about 150°. The chamber is pumped by a cryopump and a turbomolecular pump combination so as to enable experiments with a variety of gases under different conditions. The light detection includes both a direct beam monitor and polarization analyzer. The electron detection is accomplished with either a continuous channel electron multiplier or with multichannel arrays used as area detectors.

Zero kinetic energy proton and deuteron production from photoionization of H2 and D2

A zero ion kinetic energy spectrometer has been developed to study the production of near zero energy protons and deuterons from dissociative photoionization of H2 and D2. Both H+ and D+ spectra show four peaks on top of a continuum. The continuum was found to be in excellent agreement with the single center Coulomb calculation for the direct dissociation through the X 2Σ+g state of H+2. The observed structures were shown to originate from autoionization of the doubly excited Q1 1Σ+g(1), Q1 1Σ+u(1), Q1 1Σ+u(2), and Q2 1Σ+u(1) states, of which the Q1 1Σ+g(1) state is dipole forbidden.

A high resolution angle resolved photoelectron spectroscopy study of N2

This is a preliminary report on a series of measurements, using high optical resolution, on the photoionisation of the nitrogen molecule in the wavelength region 740-780 A where there are at least five Rydberg series converging onto the 1st excited state of N2+ A 2Πu. An advanced electron spectrometer system is used which provides measurements for the angular distribution parameter β for three members of the ground state of the ion, on a wavelength mesh sufficient to show variation in β over the width of the autoionising lines. This study was undertaken to assist in the identification of these series, and to encourage further theoretical work on interaction between electronic and vibrational motion in the region of autoionising resonances.