The collision-induced polarizability of a pair of hydrogen molecules

Abstract

Collision-induced light scattering, impulsive stimulated scattering, and subpicosecond-induced birefringence all depend on the transient changes Deltaalpha in molecular polarizabilities that occur when molecules collide. Ab initio results for Deltaalpha are needed to permit comparisons with accurate experimental results for these spectra and for refractive index virial coefficients and dielectric virial coefficients. In this work, we provide results for Deltaalpha for a pair of hydrogen molecules, treated at CCSD(T) level, with an aug-cc-pV5Z (spdf) basis set. Our values replace the best previous ab initio results for the variation of Deltaalpha with intermolecular separation, the self-consistent-field results obtained by Bounds [Mol. Phys. 38, 2099 (1979)] with a relatively small (3s2p) basis set for H2. For the six geometrical configurations studied by Bounds, the inclusion of correlation and improvements in the basis tend to increase both the trace Deltaalpha(0)0 and the anisotropy Deltaalpha2m of the pair polarizability. The change in the anisotropy is relatively small, but our values for the trace differ by factors of 2 or more from Bounds' results. For use in computing experimental line shapes, intensities, and virial coefficients, we have calculated Deltaalpha for 18 different relative orientations of a pair of H2 molecules, with the intermolecular separation R ranging from 2 a.u. (3 a.u. for a linear pair) to 10 a.u. The H2 bond length is fixed at the vibrationally averaged internuclear separation in the ground state r=1.449 a.u. Our results agree well with the CCSD(T) results for Deltaalpha obtained by Maroulis [J. Phys. Chem. A 104, 4772 (2000)] for two pair configurations of H2...H2 (linear and T-shaped) at a fixed internuclear distance of R=6.5 a.u. in a [6s4p1d] basis. As the intermolecular distance increases (for R>or=8 a.u.), the spherical-tensor components of Deltaalpha converge to the results from a long-range model that includes dipole-induced-dipole (DID) interactions, higher-multipole induction, nonuniformity of the local field, hyperpolarization, and van der Waals dispersion. Deviations from the first-order DID model are still evident for R between 8 and 10 a.u. in most orientations of the pair. At shorter range, overlap damping, exchange, and orbital distortion reduce both Deltaalpha0(0) and Deltaalpha(2)0 below their long-range limiting forms.

Towards understanding the hydrogen molecule in ZnO

“…which within the error bars of our measurements agrees with the values known from the literature for free H 2 [52][53][54]. Figure 8(a) shows the Raman spectra of H 2 in ZnO obtained for a sample stored and measured at 79 K with an integration time of 30 min.…”

Induced Rayleigh and Hyper-Rayleigh Spectra Pair Hyperpolarizability

“…* i) we obtain the symmetry v^t (•'.S) (b) for the octopolar A/3Q ' -component we obtain(26) and similarly for other octopolar components.This system of equations have been solved for the Afi/l (R) coefficients from the known AjS/f' '{R) given by equations (18-19) for selected intermolecular orientations and selected molecule-atom distances. Using these values we are able to compute four spherical components A/3QJ ' (R), AjSjj {R), iM, iMf A/323' (^) ^^'^ ^PAS (^) of ^^^ dipolar part of the first hyperpolarizability tensor.…”

“…Afi^cxx, ^^zzz, 3A^xzz,^^^xyy, 3A/3z", 3A/3g,j, Recently, the Cartesian CI first-hyperpolarizability surface have been computed [25] for the H2-Ar pair as a function of separation R and for the orientations 0,45 and 90 degrees-relative to the H-H bond and for rH-H= 1 -449 ao [26]. We discuss the irreducible spherical components of A/3 for C,, C2v and Ccov symmetries [27,28,29].…”

Collision-induced hyper-Rayleigh light scattering in gaseous dihydrogen-neon mixtures

“…We compute the hyperpolarizability tensors for the H 2 -Ne pair as a function of their relative separation R and for the orientations of 0 • , 45 • , and 90 • between the relative intermolecular vector R pointing from the center of mass of H 2 to the center of Ne and the H-H bond. In our computations we assume that r H−H = 1.449a 0 [20].…”