skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

Abstract

The dissociative recombination (DR) of {sup 3}He {sup 4}He{sup +} has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions in a merged beams configuration at relative energies from near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and electron cooling for 35 s, an effective DR rate coefficient at near-zero energy of 3x10{sup -9} cm{sup 3}s{sup -1} is found. The temporal evolution of the neutral product rates and fragment imaging spectra reveals that the populations of vibrational levels in the stored ion beam are nonthermal with fractions of {approx}0.1-1 % in excited levels up to at least v=4, having a significant effect on the observed DR signals. With a pump-probe-type technique using DR fragment imaging while switching the properties of the electron beam, the vibrational excitation of the ions is found to originate mostly from ion collisions with the residual gas. Also, the temporal evolution of the DR signals suggests that a strong electron induced rotational cooling occurs in the vibrational ground state, reaching a rotational temperature near or below 300 K. From the absolute rate coefficient and the shape of the fragment imaging spectrum observedmore » under stationary conditions, the DR rate coefficient from the vibrational ground state is determined; converted to a thermal electron gas at 300 K it amounts to (3.3{+-}0.9)x10{sup -10} cm{sup 3}s{sup -1}. The corresponding branching ratios from v=0 to the atomic final states are found to be (3.7{+-}1.2) % for 1s2s {sup 3}S,(37.4{+-}4.0) % for 1s2s {sup 1}S,(58.6{+-}5.2) % for 1s2p {sup 3}P, and (2.9{+-}3.0) % for 1s2p {sup 1}P. A DR rate coefficient in the range of 2x10{sup -7} cm{sup 3}s{sup -1} or above is inferred for vibrational levels v=3 and higher. As a function of the collision energy, the measured DR rate coefficient displays a structure around 0.2 eV. At higher energies, it has one smooth peak around 7.3 eV and a highly structured appearance at 15-40 eV. The small size of the observed effective DR rate coefficient at near-zero energy indicates that the electron induced rotational cooling is due to inelastic electron-ion collisions and not due to selective depletion of rotational levels by DR.« less

Authors:
; ; ; ; ; ; ;  [1]; ; ;  [2];  [3];  [1];  [4]
  1. Max-Planck-Institut fuer Kernphysik, D-69117 Heidelberg (Germany)
  2. Departement de Physique, Universite Catholique de Louvain, B-1348, Louvain-la-Neuve (Belgium)
  3. Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100 (Israel)
  4. (Israel)
Publication Date:
OSTI Identifier:
20718370
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 72; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevA.72.012712; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; BRANCHING RATIO; DIMERS; DISSOCIATION; ELECTRON BEAMS; ELECTRON COOLING; ELECTRON GAS; ELECTRON-ION COLLISIONS; ELECTRONS; EV RANGE; EXCITATION; GROUND STATES; HELIUM 3; HELIUM IONS; IONIZATION; RECOMBINATION; ROTATIONAL STATES; VIBRATIONAL STATES

Citation Formats

Pedersen, H.B., Buhr, H., Altevogt, S., Andrianarijaona, V., Kreckel, H., Lammich, L., Schwalm, D., Wolf, A., Ruette, N. de, Staicu-Casagrande, E.M., Urbain, X., Strasser, D., Zajfman, D., and Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100. Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion. United States: N. p., 2005. Web. doi:10.1103/PhysRevA.72.012712.
Pedersen, H.B., Buhr, H., Altevogt, S., Andrianarijaona, V., Kreckel, H., Lammich, L., Schwalm, D., Wolf, A., Ruette, N. de, Staicu-Casagrande, E.M., Urbain, X., Strasser, D., Zajfman, D., & Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100. Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion. United States. doi:10.1103/PhysRevA.72.012712.
Pedersen, H.B., Buhr, H., Altevogt, S., Andrianarijaona, V., Kreckel, H., Lammich, L., Schwalm, D., Wolf, A., Ruette, N. de, Staicu-Casagrande, E.M., Urbain, X., Strasser, D., Zajfman, D., and Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100. Fri . "Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion". United States. doi:10.1103/PhysRevA.72.012712.
@article{osti_20718370,
title = {Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion},
author = {Pedersen, H.B. and Buhr, H. and Altevogt, S. and Andrianarijaona, V. and Kreckel, H. and Lammich, L. and Schwalm, D. and Wolf, A. and Ruette, N. de and Staicu-Casagrande, E.M. and Urbain, X. and Strasser, D. and Zajfman, D. and Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100},
abstractNote = {The dissociative recombination (DR) of {sup 3}He {sup 4}He{sup +} has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions in a merged beams configuration at relative energies from near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and electron cooling for 35 s, an effective DR rate coefficient at near-zero energy of 3x10{sup -9} cm{sup 3}s{sup -1} is found. The temporal evolution of the neutral product rates and fragment imaging spectra reveals that the populations of vibrational levels in the stored ion beam are nonthermal with fractions of {approx}0.1-1 % in excited levels up to at least v=4, having a significant effect on the observed DR signals. With a pump-probe-type technique using DR fragment imaging while switching the properties of the electron beam, the vibrational excitation of the ions is found to originate mostly from ion collisions with the residual gas. Also, the temporal evolution of the DR signals suggests that a strong electron induced rotational cooling occurs in the vibrational ground state, reaching a rotational temperature near or below 300 K. From the absolute rate coefficient and the shape of the fragment imaging spectrum observed under stationary conditions, the DR rate coefficient from the vibrational ground state is determined; converted to a thermal electron gas at 300 K it amounts to (3.3{+-}0.9)x10{sup -10} cm{sup 3}s{sup -1}. The corresponding branching ratios from v=0 to the atomic final states are found to be (3.7{+-}1.2) % for 1s2s {sup 3}S,(37.4{+-}4.0) % for 1s2s {sup 1}S,(58.6{+-}5.2) % for 1s2p {sup 3}P, and (2.9{+-}3.0) % for 1s2p {sup 1}P. A DR rate coefficient in the range of 2x10{sup -7} cm{sup 3}s{sup -1} or above is inferred for vibrational levels v=3 and higher. As a function of the collision energy, the measured DR rate coefficient displays a structure around 0.2 eV. At higher energies, it has one smooth peak around 7.3 eV and a highly structured appearance at 15-40 eV. The small size of the observed effective DR rate coefficient at near-zero energy indicates that the electron induced rotational cooling is due to inelastic electron-ion collisions and not due to selective depletion of rotational levels by DR.},
doi = {10.1103/PhysRevA.72.012712},
journal = {Physical Review. A},
number = 1,
volume = 72,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2005},
month = {Fri Jul 15 00:00:00 EDT 2005}
}