A high-resolution synchrotron photoionization spectrometer for the study of low-energy electron-molecule scattering

Abstract

An experimental system for the study of electron-molecule scattering at high resolution is described. Synchrotron radiation from the synchrotron radiation source (SRS) at the SERC Daresbury laboratory is used to photoionize Ar at threshold (78.65 nm). The resulting photoelectrons are formed into a beam of energy spread 3.5 meV (FWHM) and crossed with a Campargue-type supersonic molecular beam. The primary electron beam energy can be varied over the range 0.04-20.0 eV. An electrostatic hemispherical monochromator with a narrow acceptance cone (+or-6 degrees ) together with a position-sensitive detector provides energy analysis of the scattered electrons. In addition a second detector comprising a cascaded pair of microchannel plates and a high-voltage anode can record without energy analysis those electrons scattered over a much wider angular range (90+or-30 degrees ). The performance of the apparatus is illustrated with data on O2, N2, SF6, NO and CO2.

Resonance and Threshold Phenomena in Low-Energy Electron Collisions with Molecules and Clusters

“…Using optimized conventional electron sources, Ibach's group (1991Ibach's group ( , 1993) have achieved energy widths down to 1 meV in electron scattering from molecules adsorbed at surfaces under ultrahigh vacuum and low current conditions. Photoelectron sources have been used for angle differential gas phase scattering experiments by Gallagher and coworkers (van Brunt and Gallagher 1978;Kennerly et al, 1981), Field et al (1988Field et al ( , 1991a and, more recently, by Gopalan et al (2003). In order to avoid the Doppler effect, differentially-pumped supersonic beam targets were used (see, e.g., Go¨tte et al, 2000).…”

“…In Fig. 14 we show an apparatus (Hoffmann et al, 2002) which has been used in this or similar form by Field and Ziesel with coworkers (Field et al, 1991a;Ziesel et al, 1993;Gulley et al, 1998a, b;Field et al, 2000;Lunt et al, 2001;Field et al, 2001a, b, c;Jones et al, 2002;Ziesel et al, 2003) to investigate total electron scattering cross-sections for a large number of molecules from low (about 20 meV) to medium electron energies (around 10 eV). Electrons are created in the source region by photoionization of ground state argon atoms (at a pressure of a few tens of mPa) through the narrow Ar(11s 0 , J ¼ 1) resonance at 78.65 nm (about 4 meV above the photoionization threshold), using focussed (10-20 mm) monochromatized synchrotron radiation.…”

Comparison of rate coefficients for rydberg electron and free electron attachment

“…The application of photoelectron sources involving VUV photoionization of ground state rare gas atoms has allowed the measurement of total, elastic and rovibrationally inelastic scattering cross sections for molecules at energies as low as 10meV with a projectile energy width around 4meV [1][2][3] and studies of electron attachment processes in the energy range 0-150 meV at typical resolutions of 6-8 meV [4][5][6]. More recently, we realized a laser photoelectron source based on resonant two-photon ionization of metastable Ar*(4s 3/'2) atoms in a collimated beam and measured the negative ion yield due to electron attachment to several molecules at sub-meV resolution in the energy range 0-170 meV [7,8].…”

Laser Photoelectron Attachment to Molecules in a Skimmed Supersonic Beam: Diagnostics of Weak Electric Fields and Attachment Cross Sections Down to20μeV

“…In addition, the effects of internal molecular energy on attachment yields can be investigated. Furthermore, we hope to perform electron scattering studies from free atoms and molecules at meV resolution by combining a directed electron beam of variable energy, extracted from a threshold photoelectron source, with a displaced skimmed supersonic beam target, building on previous work in this field [29,30].…”