A simple semiempirical model for the static polarizability of electronically excited atoms and molecules

Abstract

We present a semiempirical analytical model for the static polarizability of electronically excited atoms and molecules that requires very few readily accessible input data, including the ground-state polarizability, elemental composition, ionization potential, and spin multiplicities of excited and ground states. This very simple model formulated in a semiclassical framework is based on a number of observed trends in polarizability of electronically excited compounds. To adjust the model, both accurate theoretical predictions and reliable measurements previously reported elsewhere for a broad range of multielectron species in the gas phase are utilized. For some representative compounds of general concern that have not yet attracted sufficient research interest, the results of our multireference second-order perturbation theory calculations are additionally engaged. We show that the model we developed has reasonable (given the considerable uncertainties in the reference data) accuracy in predicting the static polarizability of electronically excited species of arbitrary size and excitation energy. These findings can be useful for many applications, where there is a need for inexpensive and quick assessments of the static gas-phase polarizability of excited electronic states, in particular, when building the complex nonequilibrium kinetic models to describe the observed optical refractivity (dielectric permittivity) of nonthermal reacting gas flows.

A simple semiempirical model for the static polarizability of ions

“…[84] In fact, there is an inverse power-function relationship between α n and N out in a given row, with the magnitude of the corresponding exponent ranging significantly (from 3 to 9). [13] However, for more accurate analytical representation of this "horizontal" trend, following Cambi et al, [158] the effective number of outer-shell electrons N eff out is to be used instead of N out to account for the additional influence of the inner-shell (core) electrons, the number of which we denote as N inn (see also reference [15] for related discussion). In doing so, for the elements starting with Li, the N eff out values can be calculated as follows:…”

“…[1][2][3][4][5][6][7] However, accurate experimental and theoretical data for this pivotal electric property are widely available mainly for neutral atomic and molecular species. [6][7][8][9][10][11][12][13][14][15] As for ions, the reliable literature values are predominately limited to singly and doubly charged monoatomic cations, [16][17][18][19][20][21][22][23] whereas both for highly charged atomic cations and especially for anions (both atomic and molecular) there is a lack of established data on polarizability. Indeed, the information available in the literature on the isotropic (scalar) polarizability values for multiply charged atomic species is essentially fragmentary, [16,21,22,[24][25][26] and the polarizability estimates for negative monoatomic ions reported elsewhere can differ by tens of percent and even several times.…”