On the Refractive Index of a Gas under High-Thermal-Nonequilibrium Conditions

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

“…[24,25,40,[45][46][47][48][49][50][51][52][53] In this respect, it is not surprising that as a result of numerous experimental and theoretical efforts, a vast body of knowledge on the electric properties of atoms, molecules, atomic and molecular clusters has been gathered to date, [6][7][8]13,20,39,[52][53][54][55][56] but most of these data refer to species in the lowest (ground) electronic states, predominantly populated at low (room) temperature, whereas disappointingly little is known about the effect of electronic excitation on the electrical response properties of multielectron systems. Meanwhile, appreciable electronic excitation of the gaseous components occurs both with thermal heating of gas to high temperatures (e.g., in thermal plasma) and under essentially nonequilib-rium conditions relevant to post-shock [57][58][59][60][61][62][63][64] and expanding nozzle [60,61,65] flows, middle and upper layers of terrestrial and extraterrestrial atmospheres, [57,58,[66][67][68][69] absorption of highpowered laser radiation in gaseous media, [16,57,…”

“…[21,22,88,122] Unfortunately, this promising methodology is expected to work well only for states of certain types of excitation, [22,122,129,130] with the success of TD-DFT in the reliable estimation of the molecular electric properties depending heavily on the choice of the DFT functional. [21,22,87] In light of the above, for diverse applications, especially, when constructing the complex nonequilibrium kinetic models with a large set of species, intended to precisely describe the observable optical refractivity (dielectric permittivity) [30,64,112,131] and transport properties [116][117][118][119] of nonthermal reacting gas flows, it would be highly convenient to have the simple theoretical tools that adequately predict the effect of electronic excitation on the polarizability and dipole moment (if present) of molecules and atoms. Such tools or analytical models would also be useful for critical evaluation of known and sometimes contradictory experimental and theoretical data on the electric properties of excited species.…”