Collisions of cold antiprotonic helium atoms and ions with ordinary helium atomsстатья
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Дата последнего поиска статьи во внешних источниках: 9 сентября 2021 г.
Аннотация:We consider two types of collisional processes with excited antiprotonic helium systems. (i) Transitions between hyperfine structure sublevels in (\bar{p}He^{+})_{nLFJ} are considered
at T =< 25 K using the coupled-channels method and a model of scalar and tensor interactions
between antiprotonic and ordinary He atoms. Inelastic cross sections for the single and double spin-flip transitions are less than elastic ones by four and seven orders of magnitude, respectively. The cross sections show a resonance behaviour at E ~ 1 - 4 K, and therefore the relaxation rates, density shift and broadening of the M1 spectral lines decrease with increasing temperature from 3 to 25 K. (ii) Stark transitions and induced annihilation during collisions of the (\bar{p}He^{++})_{nl} ion with He atoms at E ~ 10 K are considered for all l-states at n ~ 30 in the framework of the coupled-channels method. In order to take into account complex energy shifts of the ns and np-states, we introduce modified boundary conditions in these channels. The main contribution to elastic scattering, Stark transitions and induced annihilations during collisions comes from the long-range polarization interaction. Admixtures of ns and np-states to nl-states (l >= 2)during collisions induce the effective annihilation cross sections for the initial l up to 15, butdon't affect the Stark cross sections for states with nearly-circular orbits. The calculated values for both types of processes are compatible with recent experimental data.