Transitions between hyperfine structure states of antiprotonic
4He at collisions with medium atoms: interaction \emph{ab initio}
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
(pˉHe+) and
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.
Coefficients are calculated for the alignment transfer between levels of hyperfine structure (hfs) of atoms with electron momenta j=1, 1.5, and 2 and nuclear spins i=0.5, 1, 1.5, 2, 2.5, 3, and 3.5 under the influence of nonresonance collisions with atoms of a foreign gas. The results are tabulated. A concrete application of the results is illustrated in calculating numerical values of the effective cross sections for collisional transfer of alignment between hfs levels of the first excited n
sup2P
sub3/
sub2 state of rubidium and cesium atoms. (AIP)
The contributions of the relaxation of electronic polarization moments of various orders κ to the probabilities for the population transfer between the hyperfine-structure levels of an atom under the action of collisions are studied. It is shown that the contributions of higher electronic polarization moments with κ > 2 are comparable with the contributions of the orientation (κ=1) and the alignment (κ=2) or even exceed them in magnitude. This opens up the possibility of studying the collisional relaxation of higher polarization moments which are usually not observed and not involved in the emission and absorption of light under dipole transitions. The bounds for the allowable values of the rate constants for the collisional relaxation of higher polarization moments are obtained from the condition for nonnegativity of the total probabilities of population transfer between different hyperfine-structure levels under the action of collisions.