Rotationally inelastic cross sections, rates and cooling times for para-H2 +, ortho-D2 + and HD+ in cold helium gas

Abstract

Abstract. In the present work we discuss the dynamical processes guiding the relaxation of the internal rotational energy of three diatomic ions, the para-H + 2 , the ortho-D + 2 and the HD + in collision with He atoms. The state-changing cross sections and rates for these Molecular Hydrogen Ions (MHIs) are obtained from Close Coupling quantum dynamics calculations and the decay times into their respective ground states are computed by further solving the relevant time-evolution equations. The comparison of the results from the three molecules allows us to obtain a detailed understanding, and a deep insight, on the relative efficiencies of the relaxation processes considered.

Shape and strength of dynamical couplings between vibrational levels of the H2 +, HD+ and D2 + molecular ions in collision with He as a buffer gas

“…A more extended discussion of the variety of inelastic cross sections in the low temperature region which we have obtained for the present systems has been presented in a separate publications [20,26]. We therefore refer the interested reader to it for further details.…”

Quantum state preparation of homonuclear molecular ions enabled via a cold buffer gas: An ab initio study for the H2+ and the D2Schiller1, Kortunov2, Vera3 et al. 2017Phys. Rev. A293290View full textAdd to dashboardCite

“…For para-H 2 + we performed exact scattering calculations, including the electron-spin-rotation coupling s e · N. We repeated them by treating the molecule as a pseudo-1 system (i.e., ignoring electron spin and therefore ignoring the spinrotation coupling). We compared the cross sections for both cases (summed over the spin states in the exact treatment) and found that they agree within 20%, mostly within 10% [46]. Thus, the spin dependence of the cross sections can be neglected for the present purpose.…”

“…Here we limit ourselves to MHIs in the ground vibrational level v = 0. The detailed features of the potential are analyzed elsewhere [46]. Multipolar coefficients up to λ = 20 were included.…”

“…Rotational excitation processes N → N > N are seen to be energetically suppressed at low temperature, since the kinetic collision energy is insufficient for providing the difference in rotational energy between final and initial level, amounting to 42 K × [N (N + 1) − N (N + 1)]. The deexcitation rates for N → N − 2 are larger than the rates for N → N − 4 [46]. For excitation, the difference is a factor 10 or more.…”

Dynamics of molecular systems

“…Schaupp et al [1] reported an investigation of the correlated electron-nuclear dynamics in a dissociating model system, using both classical and quantum mechanical methodologies. A study of the relaxation dynamics of the internal rotational energy of the diatomic ions para-H + 2 , orto-D + 2 , and HD + in collision with cold He atoms has been presented by Hernández Vera et al [2]. A comprehensive analysis of the vibrational structure of the CO 2 system applying a polyad-preserving algebraic approach was presented and discussed by Bermudez-Montaña et al [3].…”