Transfer of a weakly bound electron in collisions of Rydberg atoms with neutral particles. I. Long-range interaction eff
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Transfer of a Weakly Bound Electron in Collisions of Rydberg Atoms with Neutral Particles. I. LongRange Interaction Effects in the Ionic–Covalent Coupling V. S. Lebedev* and A. A. Narits Lebedev Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia Moscow Institute of Physics and Technology (State University), Dolgoprudnyi, Moscow oblast, 141700 Russia *email: [email protected] Received February 6, 2013
Abstract—Ionpair formation processes are studied in collisions of Rydberg atoms with neutral particles pos sessing small electron affinities. Nonadiabatic transitions from a Rydberg covalent term to an ionic term of a quasimolecule are considered using the modified Landau–Zener theory supplemented with calculation of survival factors of an anion decaying in the Coulomb field of a positive ion core. Using the technique of irre ducible tensor operators and the momentum representation of the wavefunction of a highly excited atom, exact expressions are obtained for transition matrix elements and the ionic–covalent coupling parameter. The approach developed in the paper provides the description beyond the scope of a conventional assumption about a small variation of the wavefunction of the Rydberg atom on the range of electron coordinates deter mined by the characteristic radius of the wavefunction of the anion. This allows one to correctly consider longrange effects of the interaction between a weakly bound electron and the neutral core of a negative ion in processes under study. It is shown by the example of thermal collisions of Xe(nf) atoms with CH3CN mol ecules that this is very important for a reliable quantitative description of anion formation with a low binding energy. The results are compared with experiments and calculations performed within the framework of a number of approximate methods. DOI: 10.1134/S1063776113100154
1. INTRODUCTION A number of extensively developed directions in modern atomic and molecular physics and spectros copy are closely related to studying the mechanisms of various collisional and radiative processes proceeding at very large distance between particles, as well as to the investigating longrange interaction effects in weakly bound systems. Examples of processes involv ing very large atomic systems are transitions between highly excited levels, the ionization of Rydberg atoms in collisions with charged and neutral particles [1–4], and collisions between Rydberg atoms [5, 6]. Other examples are recent extensive studies of the formation of Rydberg atoms upon threeparticle and radiative recombination in collisions of ultracold atoms [7, 8]. Prominent examples of extremely weakly coupled sys tems are diatomic and triatomic molecules with an internuclear distance of 103–105 a.u. consisting of a Rydberg alkalimetal atom and groundstate alkali atoms produced in an ultracold gas [9, 10]. Of great interest are studies [11–14] of largeradius “heavy” Rydberg systems consisting of positive and negative ions in the weakly bound state. The
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