Intermolecular Interactions by Perturbation Theory

Shift and broadening of resonance lines of antiprotonic helium atoms in liquid4He

“…The very good agreement of the theoretical results of Refs. [5,25] with the experimental data taken at a broad range of helium gas densities up to 127 g/l should be attributed to (1) the use of an accurate pair-wise state-dependent potential for the interaction of antiprotonic and ordinary helium atoms, calculated ab initio with the symmetrized Rayleigh-Schrödinger theory [6]; (2) the use of curvilinear classical trajectories of the perturbers determined by the interaction potential for the initial state of the transition; and (3) the fact that the conditions which justify the impact approximation and the approximation of binary collisions -typical collision duration smaller by an order of magnitude than the average interval between collisions, emitter excitation energies much larger than the thermal collision energies, uncorrelated motion of the perturbers, etc. -are satisfied for the densities and temperatures in consideration.…”

“…These high-accuracy goals required various systematic effects to be accounted for, the density broadening and shift of the spectral lines being among the most important among them [4]. The density effects have been evaluated for a gaseous target in the semiclassical approach [5] using a pairwise interaction potential of an antiprotonic and an ordinary helium atom, calculated ab initio in the frame of the symmetrized RayleighSchrödinger theory [6], and the results were in agreement with the experimental data taken at helium gas densities up to 127 g/l [1]. The attempts of the ASACUSA collaboration at CERN for the laser spectroscopy of antiprotonic atoms in liquid helium [7] made us revisit the subject, since the collective degrees of freedom in the liquid phase (sound waves in the liquid consisting of the neutral 4 He atoms) provide a new mechanism for shifting and broadening the atomic spectra, in addition to those investigated in gaseous helium.…”

Convergence radii of five intermolecular perturbation theories applied to the interaction between two hydrogen atoms

“…For H 2 it appears that we can increase the convergence radius of the cPA and ZI theories without limit by increasing c. This is not the case for all systems [23]. For LiH, and presumably for more complex molecules, branch points appear at -values having negative real parts.…”

“…When R is so large that exponential contributions to the matrix elements can be neglected we find that the diagonal elements of the Hamiltonian in (18) are given by Eqs. (22) and (23). The same expressions are valid for the corresponding elements of the cPA and ZI Hamiltonians.…”

A SAPT Study of the H2O X2 Complexes; X = H, N and F

“…The SAPT methodology and its applications are discussed in several review papers. [13], [14], [15], [16], [17] In SAPT, the total Hamiltonian for the dimer is…”