Stochastic simulations of collisional-radiative processes in Rydberg plasmas

Rydberg plasmas have been identified as a source of radio recombination lines coming from H II nebulae, and are also a key element in the understanding of the evolution of the Universe during the recombination era when the first neutral atoms were formed and when radiation decoupled from the matter sector. Several processes govern the dynamics of recombination of Rydberg atoms that eventually lead to the creation of atoms in the ground state. Results are presented contrasting energy transfer and angular momentum transfer in collisions of Rydberg atoms with protons and electrons. These results, as well as the interaction of Rydberg atoms with radiation background, determine the evolution of populations of various states simulated using a stochastic algorithm, inspired by the kinetic Monte-Carlo method invented by D. Gillespie for computing chemical reaction rates. The chemical reaction rate differential equations define the average dynamics of populations involved in a network of reactions. In contrast, stochastic simulation provides mode detailed information about the distribution of atomic level populations.