W R Newell

Total cross sections for metastable excitation in the rare gases

The authors present total absolute cross sections for metastable production in the rare gases by electron impact excitation, from threshold to 140 eV. Detailed comparison is made with previous experimental and theoretical work. The effects of atomic recoil in the detection process are discussed.

ABSOLUTE VIBRATIONALLY ELASTIC CROSS-SECTIONS FOR ELECTRONS SCATTERED FROM WATER-MOLECULES BETWEEN 6 EV AND 50 EV

The authors report absolute vibrationally elastic differential cross sections for electrons scattered from water in the energy range 6-50 eV. From an extrapolation of the differential cross section data, absolute integral and momentum transfer cross sections have also been obtained. For incident electron energies above 20 eV and below 100 eV there exists only one previous report of differential cross sections (Danjo and Nishimura (1985)). Significant discrepancies have been found in this region between the cross sections reported by Danjo and Nishimura and those obtained in the present work.

ELASTIC AND INELASTIC-SCATTERING OF ELECTRONS BY METHANE AND ETHANE

Absolute elastic and inelastic differential cross sections for electrons scattered from methane and ethane have been measured for incident electron energies from 7.5 to 20 eV and scattering angles from 32 degrees to 142 degrees . The measurements were made using an electron spectrometer, incorporating hemispherical electrostatic energy analysers, and a crossed beam of target molecules. The cross sections for both molecules are generally in good agreement with other relevant experimental measurements. The methane cross sections are compared with recent theoretical results; no comparable calculations are available for ethane.

Multielectron-dissociative-ionization of by intense femtosecond laser pulses

The first detailed observations of the multielectron-dissociative-ionization of sulphur hexafluoride have been made using 60 fs laser pulses at 750 nm and . The fragmentation pattern displays features similar to those found in experiments with diatomic and triatomic molecules, such as a tendency towards symmetrically dissociative channels and fragment kinetic energies which for all channels are consistent with a Coulomb explosion at a single, critical, internuclear separation.

Fast-beam study of H2+ ions in an intense femtosecond laser field

A fast beam of H2+ ions, produced from a low energy ion accelerator, has been used for the first time in intense laser field experiments. The technique has enabled neutral dissociation products to be analysed and detected for the first time in such studies. Energy spectra of neutral and ionized fragments, product yields as a function of focused laser intensity and angular distributions of neutral dissociation products have been measured. Significant differences are observed between the present results and those obtained from experiments involving neutral H2 molecules. These differences are indicative of the precursor H2 molecule playing an important and hitherto neglected formative role in the laser-induced fragmentation processes.

Total cross section measurement for the metastable state in CO

An absolute integral cross section measurement for the electron-impact excitation of the CO(a) state is presented, which has been normalized to the theoretical work of Morgan and Tennyson. A comparison is made with previous experimental work and current theory, and a new determination for the magnitude of the cascade contribution into the a state has been made.

Electron impact total excitation cross section of the a 1Πg state of N2

The normalised total cross section for the excitation of the 1 Pi g metastable state in N2 is measured using a time of flight technique for incident electron energies from threshold to 150 eV. Comparison is made with theory and experimental work both for cross section and lifetime measurements.

Differential oscillator strengths produced by electron impact energy-loss spectroscopy of ozone

Electron impact spectroscopy has been used to obtain energy-loss spectra for ozone over an energy range 3.75-12.5 eV. The differential oscillator strength (DOS) is obtained from the O3 energy-loss spectrum and compared with the DOS obtained from optical measurements. For energy losses up to 9.75 eV the present work agrees well with the previous optical measurements but for higher values the DOS obtained in the present work is seen to deviate by up to 20% from the values obtained from the optical data. Oscillator strengths for several transitions have also been calculated from a summation of the DOS and comparisons are made with optically and theoretically obtained values.

Electron impact dissociation of N2O

The dissociation of N2O into neutral metastable fragments by electron impact has been studied for incident electron energies from threshold to 120 eV. A number of dissociation channels have been observed which produce N2(a 1 Pi g) and O(5S) metastable fragments. The kinetic energy spectra and excitation functions for both these metastable species are measured and the mechanism for N2(a 1 Pi g) production is discussed in detail.

Multi-pulse scheme for enhancing electron localization through vibrational wavepacket manipulation

A novel scheme for enhancing electron localization in intense-field dissociation is outlined. Through manipulation of a bound vibrational wavepacket in the exemplar deuterium molecular ion, simulations demonstrate that the application of multiple phase-locked, few-cycle IR pulses can provide a powerful scheme for directing the molecular dissociation pathway. By tuning the time delay and carrier–envelope–phase for a sequence of pulse interactions, the probability of the electron being localized to a chosen nucleus can be enhanced to above 80%.