Mg+(3p) excitation in slow Mg+?Ar collisions: Some remarks concerning the mechanism for Mg+(3p) excitation

Abstract

The probability and the amplitudes (2,)~-parameters) for exciting the magnetic sublevels of Mg+(3p) in collisions with Ar-atoms have been computed within the coupledchannel impact parameter approximation. An excitation mechanism is found which accounts for most of the pecularities observed in the energy and impact parameter dependence of the 2,z-parameters for this collision system: the a3sMg + orbital acquires 3d-character at internuclear distances <1.8 a.u. and by strong rotational coupling among the 3d-molecular orbitals in this region primarily the 3dn MO becomes populated. The final distribution among the magnetic sublevels of Mg+(3p) is determined by the rotational coupling at intermediate and large internuclear distances (>3 a.u.) between the cr3p and ~3p magnetic substates of Mg+(3p).

Theoretical study of the 3p-excitation in Mg+ and Mg0-inert gas collisions

“…Transitions between the adiabatic states are solely caused by the dynamical couplings. The expansion coefficients for t= ~ give the excitation amplitudes and consequently X and # with respect to the rotating internuclear axis [1]; if desired these amplitudes can be transformed to the primary beam axis as new quantisation axis furnishing new values 2 and Z. The linear polarisation and the integral excitation cross section as a function of the collision energy were computed from the probabilities for excitation of the different magnetic substates by integrating over all impact parameters.…”

“…Moreover, for Mg ~ -Ar computations of potential curves have appeared recently [5]. This work is an extension of that presented in [1]: using the data of [8,9] we can now choose the model parameters for (i) exclusively from the lowenergy results which are not affected by (ii). On the other hand, the couplings for (ii) have already been calculated for Mg +-He [10]; it will be shown in Sect.…”

“…1) can account for many of the features observed experimentally. We will adopt this mechanism for Mg +, Mg~ At, and Kr, and assume as in [1] Ly is the component of the orbital angular momentum perpendicular to the collision plane. For a number of quasi-one-electron systems ^/(R) possesses a maximum when the internuclear distance is about equal to the radius of the valence orbital.…”

“…In [1] we have attempted to reproduce experimental results [2][3][4] for the (3 s-3 p) excitation in Mg + -Ar collisions by applying the coupled channel impact parameter method. Only mechanism (i), molecular orbital transitions at small internuclear distances, was considered; mechanism (ii), the direct interaction at large internuclear distances between the Mg+-valence electron and the inert gas atom was neglected.…”

“…2 that such couplings can be predicted from these values with some confidence also for other Mg + and Mg~ gas combinations. The computations reported in this work served the purpose to find out (1) whether all characteristic features in the Mg+(32p) and Mg~ excitation in Mg +, Mg~ gas collisions can be understood when both (i) and (ii) are included simultaneously and (2) whether both the Mg + and Mg~ for the same inert gas atom can be fitted with the same set of model parameters. The only difference between the ionic and the neutral systems will then be the two times higher chance to excite a valence electron in the doubly occupied 3s orbital in the neutral Mg-atom.…”