Erratum: Collisional ionization and excitation of H 2 : Two-electron processes

2000

The relative cross section for the excitation of the 2pπ u state of H + 2 as a function of the orientation of the internuclear axis is measured and calculated. 400 eV electrons bombard an H 2 target. Electrons scattered at 18 • with an energy loss of 41 eV are detected in coincidence with H + fragment ions of energy 4.9 eV. Measurement of the scattering angle and energy loss establishes the momentum transfer vector of the collision K and the scattering plane. The angular distribution of 4.9 eV H + ions relative to K is recorded. Because the rotation time of H 2 is long compared to the dissociation time, it follows that the H + ions leave the collision region along the line of the internuclear axis at the time of the collision. The relative cross section peaks when the internuclear axis is perpendicular to K. Calculations predicting the shape of the angular distribution fit the data.

Section: Discussionmentioning

confidence: 99%

Excitation of the 2ppi_ustate of H₂⁺as a function of alignment of the molecular axis

2000

“…If autoionization does occur, then it is possible to form an H + 2 ( 2 + g ) ion in its vibrational continuum. If this happens, then the H + 2 dissociates into H + H + with the kinetic energy of each fragment in a range of 0 to about 8 eV (Edwards et al 1990).…”

Section: Introductionmentioning

confidence: 99%

“…We selected 2 eV ions. These ions are high enough in energy to be separated from the very low energy ions coming from excitation of ground state H + 2 (Edwards et al 1990). Also, they are low enough in energy so as not to overlap with the H + ions produced by excitation of excited states of H + 2 that dissociate into H + H + .…”

Section: Introductionmentioning

confidence: 99%

Excitation of the Q₁¹Σ_g⁺doubly excited state of H₂by electron impact

2001

400 eV electrons were used to excite the autoionizing state Q 1 1 + g of H 2 . The relative cross section was measured as a function of: (1) the angle between the internuclear axis and the momentum transfer vector of the collision; and (2) energy loss for a fixed orientation of the molecular axis in the laboratory frame. In the first set of measurements electrons scattered at 18 • with an energy loss of 29 eV were detected in coincidence with a 2 eV H + ion resulting from dissociation following autoionization. The angular distribution of the 2 eV ions was recorded and fitted to calculated values. A maximum was found when the internuclear axis was aligned with the momentum transfer vector. Secondly, the relative yield of 2 eV H + ions was measured as a function of energy loss in the electron-H 2 collisions. Energy loss ranged from 23 to 35 eV. The lowest lying Q 1 1 + g , 1 + u and 1 g were included in the calculated fit to the data.

“…This gives 0.13, 0.38 and 0.46 for the ratios of the 2pπ u , 2sσ g and the doubly ionized states to the 2pσ u state, respectively. Next, these contributions are weighted by estimates of their excitation cross sections relative to the 2pσ u cross section (Edwards et al 1990). This gives weighting factors of 0.35, 0.51 and 0.11 to multiply, respectively, the ratios given above.…”

Section: Discussionmentioning

confidence: 99%

“…Thirdly, measurement of the energy loss and angle of scattering of the incident electron determines the scattering plane and the momentum transfer of the collision, as is done, for example, in (e, 2e) experiments (see Lermer et al 1997 and references therein). Edwards et al (1990Edwards et al ( , 1991 reported the ionization with excitation of H 2 by equivelocity electrons and protons. In those measurements the internuclear axis was fixed at 90 • relative to the beam direction and the scattered electron was not detected.…”

Section: Introductionmentioning

confidence: 99%

Excitation of the 2psigma_ustate of H₂⁺as a function of energy loss

Mangan

et al. 1999

The relative cross section for the excitation of the 2pσ u state of H + 2 by 400 eV electrons as a function of energy loss has been measured and calculated. Electrons scattered at 18 • with energy losses ranging from 30 to 72 eV were detected in coincidence with H + ions of 7.7 eV. The H + ions were detected at 72 • relative to the beam direction. Because of the rapid dissociation of the excited state, it follows that the detected ions were produced by target H 2 molecules with internuclear axes oriented at 72 • . The relative cross sections were calculated using prolate spheroidal coordinates and fitted to the data with one parameter. The general shape of the energy-loss curve is in agreement with the measurements.