Ab initio and molecular-dynamics studies on rare gas hydrides: Potential-energy curves, isotropic hyperfine properties, and matrix cage trapping of atomic hydrogen

摘要

Ground-state potential-energy curves and distance dependent isotropic hyperfine coupling (IHC) constants for ground-state H-RG (= Ne, Ar, Kr, Xe)a re obtained at CCSD(T) (coupled-cluster single double triple) and MP4(SDQ) (fourth-order Moller-Plesset single double quadruple) levels, respectively, with an augmented basis set aug-Stuttgart (RG)/aug-cc-pVQZ (H), The obtained R_m and #epsilon# for NeH: 3.45 a AND -1.36 meV; ArH: 3.65 A and -3.48 meV; KrH: 3.75 A and -4.32 mEV; HeX: 3.90 A and -5.22 meV. The computed pair potentials are utilized in classical molecular-dynamics simulations of H-RG lattices. Along the classical trajectory, the many-body perturbation on the H atom hyperfine coupling constant is computed by pair-wise addition of the individual RG-H contributions obtained from the present quantum-chemical calculations. The computed IHC shifts are compared with electron paramagnetic resonance (EPR) spectra obtained in low-temperature matrix isolation experiments. For most cases this theoretical treatment agrees very well with the experimental and confirms the previous site assignments. However, for H-Xe, the theory would suggest stability of both interstitial O_h and substitutional sites, whereas only one site is observed in the experiment. Based on the present calculations this site can be assigned as a nearly undistorted substitutional site.