G C King

Carbon K-shell excitation in small molecules by high-resolution electron impact

The excitation of 1s carbon electrons has been observed in CO, CH4, CF4, CO2, COS, C2H2 and C2H4 by means of the electron energy-loss technique with high resolution (70 meV in the 300 eV excitation energy range) and at an incident electron energy of 1.5 keV. The energies, widths and vibrational structures of excited states corresponding to the promotion of 1s carbon electrons to unoccupied valence and Rydberg orbitals have been obtained. The validity of the equivalent-core model, and the role of resonances caused by potential barriers, are discussed.

Investigation of the energy and vibrational structure of the inner shell (1s)−1(π2p)1Π state of the nitrogen molecule by electron impact with high resolution

Abstract The vibrational structure of the (1s) −1 (π2p) 1 Π inner shell excited state of N 2 has been observed, enabling the decay width and the shape of the potential function of the state to be deduced. The validity of the equivalent core model is discussed.

The observation of electric-dipole-forbidden inner-shell transitions in N2 and Ar by the electron energy-loss technique

By using low-energy electron impact excitation the authors have observed the first example of an inner-shell single-to-triplet transition, namely the transition from the ground state to the (1s)-1( pi 2p) 3 Pi state of N2. The parameters omega e and Re of the triplet state have been deduced from the observed vibrational structure of the transition. The parity-forbidden transition to the (2p32/)-14p state of Ar has also been studied, and the intensity of this transition relative to that of the electric-dipole-allowed transition to the (2p32/)-14s state has been measured as a function of the incident electron energy.

Nitrogen K-shell excitation in N2, NO and N2O by high-resolution electron energy-loss spectroscopy

The excitation of nitrogen 1s electrons has been observed in N2, NO, and N2O by using the electron energy-loss technique at an incident energy of 1.5 keV, and with an energy resolution of 0.075 eV. The energies, widths and vibrational structures of the inner-shell excited states have been obtained. The spectroscopic constants (internuclear separation Re, vibrational constants omega and omega x and quantum defect delta ) of the inner-shell excited states of N2 have been derived and have been found to be similar to those of the equivalent core states. The energies and vibrational structures of the inner-shell excited states of NO and N2O have also been interpreted in terms of the equivalent core model.

Electron impact excitation of inner-shell excited states of CO

The design of an electron impact spectrometer for use in inner-shell studies of atoms and molecules is described. The use of the spectrometer to investigate inner-shell excited states of CO is reported. These states include the lowest lying valence states, (1s sigma C)-1(2p pi )1 Pi and 3 Pi , Rydberg states below the 1sC ionisation potential and doubly excited states above the ionisation potential.

Inner-shell and outer-shell excitation of HCl, HBr and Br2 by electron impact with high resolution

Electron impact excitation has been used to observe inner-shell and outer-shell excitation in HCl, HBr and Br2. Inner-shell energy-loss spectra have been obtained corresponding to excitation of a 2p electron in HCl and a 3d electron in HBr and Br2, at an incident energy of 1500 eV and with a resolution of typically 75 meV. The spectra are characterised by broad continua corresponding to excitation to unbound valence orbitals, and higher energy discrete structure corresponding to excitation into Rydberg orbitals. Assignments of these structures have been made and the binding energies of the inner-shell electrons have been deduced. Outer-shell, energy-loss spectra have been obtained in HBr and HCl under similar conditions.

Resonance structure in elastic electron scattering from helium, neon and argon

High energy-resolution spectra of electrons scattered elastically from helium, neon and argon atoms have been obtained as functions of scattering angle and of incident electron energy. In addition to the well known levels of the lowest configurations of the temporary negative ions (resonances), the authors observe structures at energies close to those of the (core)np5(n+1)s levels of neon and argon. These structures are attributed to resonances having configurations (core)np5((n+1)s(n+1)p3P). By calibration against features occurring at known energies in the elastic scattering spectra and also metastable excitation spectra they determine accurately the energies of the observed resonances.

Photo double ionization spectra of CO: comparison of theory with experiment

High level ab initio calculations have been undertaken of potential energy curves of CO2+ (and for the CO neutral ground state). The accuracy of the potentials was tested by a synthesis of the available vibrationally resolved threshold photoelectrons in coincidence (TPEsCO) and time of flight, photo electron photo electron coincidence (TOF-PEPECO) spectra of CO2+. Good agreement was found between experimental and theoretical spectra once relative energies of the calculated double ionization energies were slightly adjusted (by approximately 1%) to match experiment. Vibrational separations within individual electronic states are very well reproduced (the worst error is 0.07%).

Energy and time resolution of the 180 degrees hemispherical electrostatic analyser

The energy resolution and transit time spread of the 180 degrees hemispherical electrostatic analyser for nonrelativistic electrons or ions have been computed. The results have been expressed in terms of the dimensions of the analyser and the parameters describing the input particle beam for a large range of possible configurations. The predictions for a particular electron analyser have been tested experimentally and good agreement has been obtained.

Measurements of elastic electron scattering in the backward hemisphere

A new experimental method is described which allows the range of scattering angles to be extended to cover the whole of the backward hemisphere, i.e. up to , in measurements of elastic electron scattering. This is achieved by adding a localized magnetic field to the interaction region of a conventional electrostatic electron spectrometer. Measurements are presented of the differential cross section from 30 - for elastic scattering of electrons by argon at an energy of 10 eV, and of the resonance structures due to the states of at the fixed scattering angles of , and .