A General Quantum Mechanical Method to Predict Positron Spectroscopy

Abstract

The nuclear-electronic orbital (NEO) method was modified and extended to positron systems. NEO - second-order Moeller-Plesset perturbation (MP2) energies and annihilation rates were calculated for the positronium hydride (PsH) system, and the effects of basis set size on correlation energies captured with the NEO-MP2 and NEO-full configuration interaction (FCI) methods are compared and discussed. Equilibrium geometries and vibrational energy levels were computed for the LiX and e+LiX (X = H, F, Cl) systems at the MP2 and NEO-MP2 levels. It was found that anharmonicity plays a significant role, specifically in the differences between the vibrational energy levels of the LiX and e+LiX systems. The implications of these results with respect to VFR for these systems is discussed. The positron lifetime in potassium dodecahydrododecaborate methanolate, K2B12H12·CH3OH, was measured to be 0.2645±0.0077 ns. Quantum mechanical calculations reveal a spherically symmetric positronic wavefunction, with a peak in the positron density at the outside edge of the hydrogen atom cage. The experimentally determined annihilation rate corresponds to an effective number of electrons of 1.88, indicating that there is significant positron density both inside and outside of the B12H122- cage