Formation and photodetachment of cold metal cluster negative ions
A general method is described for the formation of cold metal cluser negative ion beams which serve as excellent sources for photodetachment experiments. The method involves the pulsed laser vaporization of a metal target at the throat of a pulsed supersonic helium expansion. By the optimization of source conditions, intense beams (greater than 10/sup 5/ ions/pulse) of both positive and negative ions are produced routinely. Ionization of the metal cluster molecules, either during vaporization or by irradiation with 193 nm light, occurs prior to supersonic expansion and produces a cold plasma entrained in the neural flow that is renitent to stray electric and magnetic fields, unlike photoions produced in the collisionless downstream molecular beam. The enhancement of the negative ion flux by 193 nm irradiation is believed to be evidence for efficient electron attachment of low energy photoelectrons generated in the nozzle region. This attachment process, however, is apparently not effective for molecules containing less than approx.4 metal atoms. Laser irradition of mass-selected cluster anions extracted from these cold ion beams reveal that photodetachment of the metal cluster negative ion is always the preferred pathway, even when fragmentation of the ion is possible. This new negative ion production technique should therefore permit measurement of both electron affinities and photoelectron spectra as a function of cluster size and composition.
- Research Organization:
- Rice Quantum Institute and Department of Chemistry, Rice University Houston, Texax 77251
- OSTI ID:
- 5222946
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 83:8
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
ION BEAMS
BEAM PRODUCTION
METALS
PHOTOIONIZATION
ANIONS
EVAPORATION
LASER RADIATION
NOZZLES
BEAMS
CHARGED PARTICLES
ELECTROMAGNETIC RADIATION
ELEMENTS
IONIZATION
IONS
PHASE TRANSFORMATIONS
RADIATIONS
640301* - Atomic
Molecular & Chemical Physics- Beams & their Reactions