Charge transfer in collisions of the effectively-one-electron isocharged ions Si3+,C3+, and

Abstract

In a recent paper [Phys. Rev. A 77, 064702 (2008)], Bruhns et al. reported on an experimental investigation of charge transfer in collisions of Si 3+ ions with atomic hydrogen and compared the energy dependence of the transfer cross sections with published theoretical results and with earlier experimental results for other effectively-one-electron isocharged ions, including C 3+ and O 3+ . These authors observe that these three ions all have the structure of a single electron outside a closed subshell and thus might be expected to behave similarly. However, their results show quite different behavior, and they conclude that the influence of quantum-mechanical effects from the ionic core is clearly seen. We have investigated theoretically three collision systems, Si 3+ , C 3+ , and O 3+ with atomic hydrogen, at projectile energies up to 10 keV/amu using the method of electron nuclear dynamics (END). In this paper we want to clarify and describe in some detail these quantum-mechanical effects by showing the time-dependent dynamics of the electrons during the collision of these three ions with atomic hydrogen. Total charge transfer cross sections were calculated for all three ions and compared with other theoretical and experimental results, showing good overall agreement. With this validation of the END description of the processes, we analyze the details of the computed dynamics of the electrons in each of the processes and illustrate the different mechanisms underlying observed differences in reaction outcomes.

Non-adiabatic effects in thermochemistry, spectroscopy and kinetics: the general importance of all three Born–Oppenheimer breakdown corrections

“…At no point in the parameter space at which significant BO breakdown occurs does the application of any partial correction lead to quantitatively accurate results, though the DC-only and FD-only approaches can yield qualitatively useful information, with the error for DC-only typically being significantly less than that for FD-only. This is particularly true for important charge-transfer systems such as 1 (DPP), 2 (Alq3), 20 and 5 (CT), as well as for spectroscopically relevant systems such 4 (BNB) and 3 ( 3 PYR). Fig.…”

“…Further, the cusp diameter is identified as the critical physical property controlling BO breakdown based on simple analytical expressions (Eqn. (19)(20)) that relate the three BO breakdown terms to each other and establish their close connection and common origin in terms of the cusp diameter. Indeed, deviations of rate constants from the predictions of transition-state theory are also shown to correlate well with the cusp diameter (Eqn.…”

“…Finding 55 conceptually enlightening and/or quantitatively accurate solutions in such cases is at the forefront of research in chemical physics, [8][9][10][11][12][13][14] involving identification and treatment of the causes for breakdown of the BO approximation. While it is possible to avoid the BO approximation by directly solving the coupled quantum electron-nuclear dynamics, [15][16][17][18][19][20] the associated computationally difficulty leads to it being much more common to start with the Born-Oppenheimer approximation, calculate potential energy surfaces, then take into account BO breakdown. Two fundamentally different strategies are in common use for the treatment of BO breakdown.…”

“…Naively, such blocking is not expected as DC arises 9,60 as the square of the FD correction (Eqn. (19)- (20)) and so is intrinsically narrower (e.g., at only SD gives a higher value of 15%; note that these are instantaneous values and that some of the density that had earlier crossed to the ES by this time has now re-crossed back to the GS. However, the complex nature of the interplay between all 3 correction terms is demonstrated by noting that FD+SD combined 45 yields only 2% on the ES at this time, the two contributions acting to largely cancel each other out, while the full calculation DC+FD+SD yields 27% on the ES so that the FD and SD terms now appear to reinforce each other.…”

Uncertainty estimates for theoretical atomic and molecular data

“…This is supported by the close agreement of the calculations of refs. [226,228] with each other and, where available, with experimental data as well. Overall, figure 15 illustrates nicely that an uncertainty estimate for a complicated collision problem should use the input from several calculations based on different theoretical methods.…”