Emission by collisional H2–He pairs at temperatures from 2 to 20 kK

Abstract

The dipole surface of H2–He collisional pairs is computed from first principles for 20 intramolecular spacings of the H2 molecule, from 0.6 to 4 Bohr; 11 separations of the H2–He pair, from 2 to 6 Bohr; and five values for the angle subtended by the intramolecular and intermolecular axes. From this dipole surface, the dipole matrix elements are obtained for all possible rotovibrational transitions |vJ〉→|v′J′〉, with v and v′=0,… ,14. Subsequently, the collision-induced emission spectra are computed for frequencies from 100 to 100 000 cm−1, at temperatures of thousands of Kelvin—a range believed to be important for various light sources of high gas densities, such as the atmospheres of “cool” stars, shockwaves, flames, rocket jets, etc. We find that at the lower temperatures considered, radiation is emitted mostly in the fundamental band of H2, while at high temperatures the collision-induced emission spectra extend into the visible, with overtone transitions involving large Δv=v−v′.

Pressure Distortion of the H2–He Collision-induced Absorption at the Photosphere of Cool White Dwarf Stars

“…To compute CIA spectra, previous investigators (e.g., Abel et al 2012;Birnbaum et al 1984;Borysow 1992;Hammer et al 1999;Meyer & Frommhold 1986) have relied on an approach combining quantum chemical computations with molecular scattering theory. In such calculations ab initio methods (e.g., Møller-Plesset calculations, coupled-cluster calculations) are used to obtain accurate potential energy (PES) and induced dipole (IDS) surfaces for the H 2 -perturber super-molecular complex in the infinite-dilution limit.…”

Systematics of Collision-Induced Light Emission from Hot Matter

“…(power/unit arae) ) σT 4 (15) number of photons ) ∫ (hν) -1 I(ν) dν ) 32π 4 3hc 3 ∫ ν 3 |µ(ν)| 2 dν ( 16) 17) The functional form of the Ar-Xe dipole moment function µ(R) is approximated as [20][21][22]32,33 The parameters are a 0 ) 9.321 × 10 -3 au, R ) 6.1714 Å -1 , and R e ) 2.8707 Å. The dipole moment of the cluster is taken as the vector sum of the contributions of the dipole of the different mixed pairs.…”

“…The emission spectrum of the cluster is then computed in terms of the Fourier transform of the dipole moment of the cluster. An alternative way of stating the computational procedure, and a way that allows a closer connection with the theory of collision-induced absorption (or emission 21 ) in mixtures is that we first Fourier transform the dipole function for each mixed pair of atoms in the cluster. When we compute |µ(ν)| 2 , the contributions of different dipoles average out and What this means is that the spectrum scales with the number of those mixed pairs that give rise to a significant dipole moment.…”

“…Current progress in the study of collision-induced (light) absorption is much concerned with obtaining accurate (and not only realistic) dipoles as functions of the interatomic distance(s). − For collisions at such high velocities where the atoms get quite close to one another and significant promotion of electrons into higher orbitals is likely, we do not even have fully reliable realistic dipole functions. Therefore we proceed in two complementary ways.…”

Sonoluminescence: how bubbles glow

“…exchange and dispersion forces, multipolar induction, and collisional frame distortion of otherwise non-polar molecules [101]. A crude model of collision-induced emission of N 2 -X pairs, with X standing for Ar, N 2 , or almost anything else, was previously applied to sonoluminescence [122], but improved, recent work on similar systems, based on rst principles [123][124][125], suggested much lower intensities; besides we now know that molecules such as N 2 cannot be expected in stable sonoluminescent bubbles [67,68,72,73]. The collision-induced emission model previously proposed [122] is not useful for an understanding of single bubble sonoluminescence in a totally neutral, dense, rare gas environment, because in the absence of the rotovibrational bands of molecules such as N 2 no collision-induced emission of visible light can be expected in single bubble sonoluminescence.…”