Inelastic low-energy collisions of electrons with HeH+: Rovibrational excitation and dissociative recombination

Abstract

Inelastic low-energy (0-1 eV) collisions of electrons with HeH + cations are treated theoretically, with a focus on the rovibrational excitation and dissociative recombination (DR) channels. In an application of ab initio multichannel quantum defect theory (MQDT), the description of both processes is based on the Born-Oppenheimer quantum defects. The quantum defects were determined using the R-matrix approach in two different frames of reference:the center-of-charge and the center-of-mass frames. The results obtained in the two reference systems, after implementing the Fano-Jungen style rovibrational frame-transformation technique, shows differences in the rate of convergence for these two different frames of reference.We find good agreement with the available theoretically predicted rotationally inelastic thermal rate coefficients. Our computed DR rate also agrees well with available experimental results. Moreover, several computational experiments shed light on the role of rotational and vibrational excitations in the indirect DR mechanism that governs the low energy HeH + dissociation process. While the rotational excitation is several orders of magnitude more probable process at the studied collision energies, the closed-channel resonances described by the high-n, rotationally excited neutral molecules of HeH contribute very little to the dissociation probability. But the situation is very different for resonances defined by the high-n, vibrationally excited HeH molecules, which are found to dissociate with approximately 90%

Cross Sections and Rate Coefficients for Rotational Excitation of HeH+ Molecule by Electron Impact

“…The agreement between the three sets of calculations are perfect to the 0 ↔ 2 transitions, while for the 0 ↔ 1 transitions the rate coefficients of Reference [10] are somewhat larger than the present result and the one from Reference [17]. For the 0 ↔ 3 transitions, the coefficients of Reference [17] are somewhat larger than the present result and the one from Reference [10]. For the 0 ↔ 4 transitions, the coefficients from the two other calculations agree with each other and are slightly larger than the present result.…”

“…The dissociative recombination of HeH + has been extensively studied both experimentally and theoretically [19][20][21][22]28]. There are no experimental measurements of cross sections for the rotational excitation of HeH + , but there are a few previous theoretical studies [1,3,10,17]. Therefore, the present results can be compared with the previous calculations.…”

“…They are compared with recently published data for the j = 0 ↔ j transitions: dotted lines are the calculations by Hamilton et al [10] and the dashed lines are those ofČurík and Greene [17]. The agreement between the three sets of calculations are perfect to the 0 ↔ 2 transitions, while for the 0 ↔ 1 transitions the rate coefficients of Reference [10] are somewhat larger than the present result and the one from Reference [17]. For the 0 ↔ 3 transitions, the coefficients of Reference [17] are somewhat larger than the present result and the one from Reference [10].…”

“…This method will be referred to below as the QDT method. It has been used in slightly different implementations in theoretical studies of rotational excitation for several molecular ions: H + 2 [14,15], H + 3 [16], HeH + [17], and CH + [18]. The molecular-frame scattering matrix in the QDT method can be evaluated in different ways.…”

“…In the present study, essentially the same theoretical method as in Reference [17] is used to represent the rotational excitation of HeH + , but the results for a larger number of rotational transitions in HeH + are obtained and an analytical fit of the thermally-averaged rate coefficients is performed, allowing the use of the data in plasma modeling.…”