Transitions between hyperfine structure states of antiprotonic $^4 \mathrm{He}$ at collisions with medium atoms: interaction \emph{ab initio}

TL;DR

This paper presents an ab initio calculation of interaction potentials and transition rates for hyperfine structure states of antiprotonic helium during collisions, providing insights into spectral line shifts and broadening.

Contribution

It introduces a detailed ab initio approach to compute interaction potentials and transition dynamics of antiprotonic helium hyperfine states during collisions.

Findings

Calculated potential energy surface for ar{p}He+He system.

Numerical solutions for transition cross sections and rates.

Comparison with experimental data and models.

Abstract

Collisions of metastable antiprotonic helium atoms with atoms of the medium induce, among other processes, transitions between hyperfine structure (HFS) states, as well as shifts and broadening of microwave M1 spectral lines. In order to obtain matrix potential of interaction between $(\mathrm{\bar{p} He} ^+)$ and $\mathrm{He}$, we have calculated the potential energy surface (PES) in the framework of unrestricted Hartree-Fock method taking into account electron correlations in the second-order perturbation theory (MP2). With this potential, the system of close-coupling equations for HFS channels is solved numerically. Cross sections and transition rates, shifts and broadening of M1 spectral lines are calculated. They are used to obtain a numerical solution of the master equation that determines the time evolution of the HFS-states density matrix. The results are compared with the experimental data and with the results of model calculation.