Electron-impact dissociative excitation of H+2: low energy studies

Cross sections for the dissociative recombination of isomeric HCN+/HNC+ ions with electrons were measured using the single-pass merged beam experiment located at the University of Western Ontario in Canada. The source conditions were varied so that an HCN+/HNC+ mixture was first studied. The HNC+ ion was then isolated via the fast ion-molecule reaction HCN++CO2HNC++CO2. The two sets of measurements, which both refer to vibrationally (and electronically) excited states of HCN+ and HNC+, exhibit differences in the magnitudes of the cross sections. Thermal rate coefficients have been calculated for both species. An attempt has been made to identify the valence states involved in the dissociation to the CN+H channel for HCN+ recombination.

Section: Experimental Chamber Meibe Isupporting

confidence: 85%

Merged beam measurement of the dissociative recombination of HCN⁺and HNC⁺

Sheehan

Padellec

Lennard

et al. 1999

“…At electron energy above the dissociation limit of the cation ground state, the DR process involves only the direct DR mechanism depicted by equation (1). Measurements of DE cross sections for hydrogen molecular cations were acquired at heavy-ion storage ring [18][19][20], by animated crossed beam method [21] and merged beam method [22]. In the case of hydrogen molecular cations the theoretical DE studies are rare [1,23,24] in the literature.…”

Section: Introductionmentioning

confidence: 99%

Electron-induced processes in H⁺₂, D⁺₂and T⁺₂

Stroe¹,

Fifirig²

2009

We investigate the isotopic effects on the cross sections of the dissociative excitation, dissociative recombination, vibrational excitation and vibrational de-excitation of the homonuclear hydrogen molecular cations with electrons of energy above the dissociation threshold of the electronic ground state. The computations were accomplished using an improved numerical code based on a previous work (Fifirig and Stroe 2008 Phys. Scr. 78 065302).

“…Their measurements are limited to the energy range from 54 to 943 eV, while the threshold is theoretically expected to be between 16 and 30 eV for the highest and lowest vibrational level, respectively. Using the merged beam technique, Yousif and Mitchell (1995) have measured the absolute total cross section for the sum of dissociative processes of H + 2 ions in the lowenergy range from 10 meV to 35 eV. One of the major problems with H + 2 (and D + 2 ) is the fact that, being a diatomic homonuclear molecule, it does not possess a permanent electric-dipole moment, so the vibrationally excited levels have extremely long lifetimes (∼10 6 s) and hence do not decay.…”

Section: Introductionmentioning

confidence: 99%

Total cross sections and kinetic energy release for the electron impact dissociation of H⁺₂and D⁺₂

Abdellahi

Jureta

Urbain

et al. 2004

Absolute total cross sections have been measured for electron impact dissociative excitation and dissociative ionization of H+2 and D+2 in the energy range 5–3000 eV. The vibrational population of the primary H+2 beam has been analysed by dissociative charge exchange on a potassium target, and is in good agreement with the measurements of von Busch and Dunn (1972 Phys. Rev. A 5 1726). Kinetic energy release (KER) distributions have been extracted from momentum analysis of the released protons and deuterons at selected impact energies. A model calculation has been performed to interpret the different spectra. Below 100 eV, the distributions exhibit a sharp peak in the range 0–1 eV that is attributed to the dissociative excitation of high vibrational levels to the 2pσu repulsive state in the vicinity of their outer turning point. This observation is consistent with the measured vibrational population extending up to v = 13, as confirmed by the appearance threshold of the dissociative ionization (DI) channel. The KER distributions exhibit a second contribution peaking between 1 and 5 eV, resulting from the admixture of the (1sσg → 2pσu), (1sσg → 2pπu) and (1sσg → 2sσg) electronic transitions. A distinctive hump is also present around 9 eV, that coincides both with the maximum of the DI contribution, and with the high-energy shoulder of the 2pπu and 2sσg contributions. The present measurements are in qualitative agreement with the previous results of Caudano and Delfosse, and are fairly well reproduced by our first-order model.