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Photoelectron study of the satellite ion states of HCl and the production of autoionizing chlorine atoms by photodissociation of HCl

The HCl+ satellite states, in the energy range 20-31 eV, have been studied by photoelectron spectroscopy. The energy resolution achieved has allowed vibrational levels to be observed for the first time which has shown the two lowest lying states to be dissociative. The use of tunable VUV radiation has provided detailed information on resonance processes occurring in the region of the ionization thresholds for the satellite ion states. These processes include neutral photodissociation producing autoionising chlorine atoms. Some of the observed atomic states are optically forbidden in transitions from the ground state of the atom.

Threshold electron impact excitation of hydrogen chloride

A high-resolution threshold-electron spectrometer was used to study excitation of HCl molecules O-10 meV above the thresholds for electronically excited states. The spectrum is obtained in an energy region from 4.2-14 eV corresponding to the excitation of lower valence states and Rydberg states below and just above the 2 Pi 3/2, 1/2, ionisation threshold. This first study of threshold excitation of HCl molecules reveals a considerable difference in relative intensities of some of the states compared with the case of higher-energy collisions. The transition into the lowest 3 Pi valence state is reported for the first time. The threshold ionisation region is discussed in terms of the superposition of the correlation-dominated direct ionisation process and the excitation function of an autoionising level decaying by releasing a zero-energy electron.

A compact catalytic converter for the production of para-hydrogen

The design and operation of a compact converter to produce a constant flow of para-hydrogen from normal hydrogen is described. The converter features a paramagnetic compound (nickel sulfate) that catalyses the conversion of ortho- to para-hydrogen at temperatures of 14-21 K. The converter has been tested by measuring rotationally resolved photoelectron spectra in the para-hydrogen produced. The percentage of the para-hydrogen species in the converted gas was determined to be >97%.

A STUDY OF PHOTOELECTRON ANGULAR DISTRIBUTIONS IN XENON USING A NEW MAGNETIC ANGLE-CHANGING TECHNIQUE

The angular distribution parameter for the Xe ion state has been studied for the Xe autoionization resonances in the energy range between 20 and 24 eV using tunable synchrotron radiation from the Daresbury Laboratory SRS. A new magnetic angle-changing technique has been used and is reported for the first time in photoionization measurements. This technique allows the angular measurements to be made without any movement of the electron spectrometer. The present measurements have been made as continuous functions of both photon energy and photoelectron ejection angle which highlights the dramatic effect of those autoionizing resonances on the angular distribution parameter.

Differential cross sections for electron impact excitation of the n = 2 states of helium at intermediate energies (80, 100 and 120 eV) measured across the complete angular scattering range (0–180°)

Differential cross sections (DCS) for inelastic electron scattering to the n = 2 states in helium have been measured at incident energies of 80, 100 and 120 eV. These DCS have been determined across the complete angular scattering range (0–180°) using a magnetic angle changer (MAC) with a soft-iron core. The convergent close-coupling (CCC), R-matrix with pseudostates (RMPS), and B-spline R-matrix (BSR) methods have been used to calculate these DCS. Agreement between the experimental data and the predictions from these highly sophisticated theoretical methods is generally good. The remaining discrepancies mainly occur at small and large angles for the triplet states 23S and 23P, whereas excellent agreement is found between 30° and 150°. The small-angle differences are likely due to contamination of the observed experimental signal from the neighbouring 21S and 21P states. The present results demonstrate the effective use of a soft-iron core MAC for DCS measurements at intermediate energies, extending the operational energy range of such devices by a factor of approximately 25.

Auger emission from Xe above and below the 4d ionization threshold

The Auger electron yield from xenon has been measured in the vicinity of the 4d inner-shell ionization threshold. Just above this ionization threshold the Auger line profile is modified by the post-collision interaction effect involving a slow photoelectron. The process is followed through threshold into a region where the photoelectron is recaptured and either shaken up/down or remains in its Rydberg orbital during the Auger decay. By measuring the electron yield as a function of both incident photon energy and electron kinetic energy a comprehensive study of these processes is made.

A photoelectron study of the rotational selectivity of vibrational autoionization of H2

Rotationally selective vibrational autoionization in molecular hydrogen has been investigated using two-dimensional photoelectron spectroscopy. Measurements of electron yield as a function of both electron and photon energy have been carried out using tuneable synchrotron VUV radiation between the upsilon =0 and upsilon =1 vibrational thresholds of H2+X2 Sigma g+, 15.45-15.70 eV. Constant rotational transition energy spectra have been extracted revealing the decay routes of autoionizing states. No large changes in the rotational quantum number of the ion core during autoionization were observed.

Iron-cored coil system for the measurement of angular distributions of charged particles

A novel coil system is described that enables the magnetic angle-changing technique to be used at higher energies. The system consists of coils of wire that are combined with specially shaped iron cores in such a way as to preserve localization of the magnetic field. The system extends the operational energy range of previous systems consisting of solenoids alone by a factor of 25. Measurements of the electron impact excitation of the n=2 states of helium are presented as an example of the use of the device.

The interpretation and application of two-dimensional photoelectron spectroscopy

Abstract The technique of two-dimensional photoelectron spectroscopy, in which photoelectron yield is measured as a function of both electron and photon energy, is explained. The appearance of autoionising resonance features is modelled under a variety of experimental conditions. Although two-dimensional spectra normally provide a large amount of detailed information, it is often necessary to extract one-dimensional spectra in order to perform comparisons with other work. The extraction procedure is considered using the specific example of constant transition energy spectra, which indicate the population of particular ion states as a function of photon energy. In addition, experimental effects that are readily visible in two-dimensional spectra, but which may be hard to identify in one-dimensional measurements, are highlighted. Representative two-dimensional spectra are presented in order to illustrate these points with real examples.

Photoelectron studies of the resonant excitation and ionization of the Kr 3d inner subshell in the low kinetic energy region

Photoexcitation of the Kr 3d to np resonances and photoionization of the 3d inner shell have been studied by measuring the emitted electrons with energies from 0 to 3 eV and from 0 to 12 eV, respectively. Intense discrete structure due to the Kr+ to Kr2+ transitions has been observed in photoelectron spectra. Assignments are proposed based on the spectator shake model and by analysis of effective quantum numbers of proposed Kr+ states. The observed energy shift and asymmetric line broadening, related to the post-collision interaction, of the Kr+ 3d-1(2D512.3) ionic states have been compared with previous experimental results and with theoretical predictions.