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

Abstract

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.

Electron impact induced dissociation of N2H+into NH+

“…This is done by scanning the analyser magnet and integrating the resulting product spectrum. This measurement also provides information on the KER distribution of the fragments [7].…”

Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues

“…Dunn [25] utilized the delta (reflection) approximation and the first Born approximation electronic excitation cross sections of Peek [26] to calculate H + 2 KER cross sections which are valid only in the high incident electron energy limit. El Ghazaly et al [18] used the more accurate square root approximation, with excitation cross sections derived from the oscillator strengths of Ramaker and Peek [27], yielding results in reasonable agreement with experiment. The lack of theoretical KER cross sections calculated using accurate collision data motivates the present work.…”

“…(9) is computationally expensive due to the large number of numerical integrations which must be performed. Following El Ghazaly et al [18], we replace the constants and the T -matrix elements in Eq. (9) with the square root of the electronic excitation cross section at incident electron energy E in :…”

“…The CCC results were in good agreement with measurements of proton-production and dissociative ionization cross sections. Utilizing these results, here we calculate the KER cross sections using the T -matrix, square root and delta approximation methods, and compare their agreement with each other and with the measurements of El Ghazaly et al [18]. Atomic units are used throughout this paper unless specified otherwise.…”

“…Many experimental measurements of the KER cross sections have been used to extract scattering cross sections [8][9][10][11][12][13][14][15][16][17][18], identify dissociative processes [8][9][10][11][12][13][14][15][16][17][18], and to determine experimental conditions [18][19][20], molecular structure [21,22] and collision dynamics [21]. The KER cross sections can be extracted from a complete close-coupling calculation that includes all degrees of freedom (electronic, vibrational, and rotational).…”