Simple analytical formulas for collisionallmixing,nchanging, and ionization of Rydberg atoms with neutral particles at thermal energy

Simple analytical formulas are given that allow the rapid estimation of cross sections for l mixing, n changing, and ionization of Rydberg atoms with atomic and molecular targets. These formulas are derived by using the quasifree-electron model and the impulse approximation. The l dependence of the cross section is accounted for only via the atomic energy. The quasielastic process of angular-momentum mixing caused by either the short- or long-range interaction between the Rydberg electron and the neutral perturber is studied and the corresponding cross sections are evaluated. The Rydberg-atom---molecule inelastic transitions (n changing and ionization) caused by the e^--dipole or e^--quadrupole interaction are investigated. It is shown that the n-changing reactions occur via quasiresonant internal-energy transfer between the two colliding partners. The influence of the relevant physical parameters is clearly stated for the three types of interaction (short-range, e^--dipole, e^--quadrupole). Comparison with more sophisticated approaches and experimental data shows that the accuracy of the formulas is about a factor of 2.