Dynamic Multipole Polarizabilities of the Rare-Gas Atoms Ne, Ar, and Kr and Long-Range Interaction Coefficients of the Rare-Gas Atoms and with H₂

Abstract

Dynamic polarizabilities and excitation energies are obtained from multireference configuration interaction wave functions. The multiconfigurational reference function is designed to represent the ground state as well as the perturbed states and the first excited state on equal footing; i.e., orbital optimization is performed in a perturbed multiconfigurational self-consistent field procedure. Furthermore, perturbed and excited multireference configuration interaction wave functions are obtained simultaneously for several frequencies of the perturbing field. Reduced three-term spectra are derived which reproduce exactly the calculated polarizabilities at the selected frequencies and very well interpolate the dynamic polarizabilities up to the first pole. These reduced spectra also serve to calculate long-range interaction coefficients. The results for both the dynamic polarizabilities and the interaction coefficients are found to be in excellent agreement with experimental values where such data exists and also with most accurate theoretical results. I. IntroductionIn this work we continue to investigate the ability of direct multireference configuration interaction (MR-CI) methods to compute reliable dynamic polarizabilities. While the calculation of static polarizabilities is rather straightforward for all quantum chemical methods by using finite fields, such an approach is not possible for dynamic polarizabilities which therefore pose a much more challenging problem. So far the influence of electron correlation on the calculation of dynamic polarizabilities has mainly been studied in the multiconfiguration self-consistent field (MC-SCF) approximation or in the context of many-body perturbation theory (MBPT), whereas CI methods have only occasionally been used. The MC-SCF applications are usually based on the multiconfigurational linear-response approach derived by Dalgaard 1 and Olsen and Jørgensen. 2 It is an direct extension of the simple and rather successful coupled HartreeFock formalism 3,4 in that the perturbed wave function is obtained as the first derivative with respect to the (time-dependent) field strength from a wave function ansatz with predefined configurational structure but field-dependent configuration and orbital expansion coefficients. This "derivative approach" has as well be applied to second-order Møller-Plesset (MP2) wave functions by Rice and Handy 5 and Hättig and He . 6 Perturbation expansions have also been used in a nonderivative "perturbational" approach, that is, by double perturbation theory up to second order in both electron correlation and external perturbation, based on a single field-independent orbital set. 7-10 While this latter method as well as the derivative MP2 method are restricted to ground states which are well approximated by a single closed-shell determinant, the MC-SCF linear response method is rather limited in the amount of dynamic correlation that can be accounted for. We believe that the highly flexible MR-CI method should be a viable tool for treating dynami...

The phenomena of radiative association and charge transfer observed in Ar ++ H and Ar + H + collisions

“…Moreover, this rare gas hydride cation has also been detected for the first time in the galaxy PKS 1823-211 by Müller et al [9]. In particular, they observed the J = 1 ← 0 transition of 36 ArH + at the frequency 617 525.23 ± 0.15 MHz and of 38 ArH + at 616 648.76 ± 0.08 MHz. Their observations led the authors to estimate an argonium presence with the isotopic ratio 36 ArH + / 38 ArH + = 3.46 ± 0.16.…”

“…The finding was the first noble gas molecule detected in the extra space, where the authors identified two 36 ArH + emission lines: one at 617.5 GHz, arising from the rotational line J = 1 ← 0, and a second at 1234.6 GHz, arising from the rotational line J = 2 ← 1. Besides, Schilke et al [2] noticed that the unspecified 617.5 GHz absorption transition observed in almost purely atomic diffuse gas was indeed due to argonium 36 ArH + . Following this, features of 38 ArH + were determined as a consequence, and it was proposed that argonium is prevalent in the interstellar medium [2].…”

“…In particular, they observed the J = 1 ← 0 transition of 36 ArH + at the frequency 617 525.23 ± 0.15 MHz and of 38 ArH + at 616 648.76 ± 0.08 MHz. Their observations led the authors to estimate an argonium presence with the isotopic ratio 36 ArH + / 38 ArH + = 3.46 ± 0.16. Müller and his collaborators even believe that ArH + may constitute a very good tracer of the almost purely atomic diffuse ISM [9].…”

“…Using the European Space Agency's Herschel Space Observatory, Barlow et al [1] reported the detection of traces of the protonated argon cation 36 ArH + , also known * Author to whom any correspondence should be addressed. as argonium, in the Crab Nebula.…”

Atomic scattering from an adsorbed monolayer solid with a helium beam that penetrates to the substrate

“…There are only minor changes from the previously calculated inelastic scattering distributions. For this system there are good models [8][9][10] for the He-H 2 and He-NaCl interactions and experimental data 7 for the phonon spectrum. In contrast, the components of the interaction model for the H 2 /KCl(001) are less well-determined and the calculations there are more exploratory in character.…”