Collisional and thermal ionization of sodium Rydberg atoms: II. Theory fornS,nP andnD states withn= 5–25

Abstract

A stochastic model of associative ionization in collisions of Rydberg atoms with ground-state atoms is presented. The conventional Duman-Shmatov-Mihajlov-Janev (DSMJ) model treats the ionization as excitation of Rydberg electron to the continuum by the electric-dipole field generated by exchange interaction within the quasi-molecular ion. The stochastic model essentially extends this treatment by taking into account redistribution of population over a range of Rydberg states prior to ionization, which is caused by nonadiabatic processes in overlapping multiple level crossings of quasi-molecular Rydberg states. The redistribution is modelled as diffusion of electrons in the Rydberg energy spectrum using a Fokker-Planck-type equation. The process of l-mixing of Rydberg states at large internuclear distances and twisting of the collision trajectories on attractive potentials are taken into account. The choice of the collision velocity distribution is also shown to be important. Associative ionization rates have been calculated for Na * * (nl) + Na collisions with n = 5-25 and l = 0, 1, 2, and compared with the available experimental data and the calculations performed using the nonlinear DSMJ model. At relatively low n the stochastic model yields a substantially better agreement with the experimental data than the DSMJ model, while the results of both models converge at large n.

The influence of -mixing processes in collisions on atoms’ populations in weakly ionized helium plasmas

“…Namely, these processes are well studied experimentally and theoretically and it was found that there is very good agreement between experimental and theoretical results [17][18][19][20][21][22][23][24][25][26].…”

“…The resonant mechanism has been successfully applied to chemi-ionization processes in alkali Rydberg's atoms collisions with their parents' ground state [16], and further for alkali atoms' collisions [17][18][19][20][21][22][23][24][25][26]. In the case of hydrogen and helium atoms, the resonant mechanism was used to analyze the chemi-ionization and their inverse chemi-recombination processes [27][28][29][30][31][32][33].…”

Autoionization of an ultracold Rydberg gas through resonant dipole coupling

“…The photoionization cross sections are evaluated using the semiclassical formula given in [19,20,21],…”

Ionization of sodium and rubidiumnS,nP, andnDRydberg atoms by blackbody radiation

“…It also induces transitions between neighboring Rydberg states, thus leading to a population redistribution [7,8,18]. For example, after laser excitation of the Na 16S state, the BBR-induced transitions populate the neighboring n ′ P states [ Fig.…”