Mechanism of and alignment effects in spin–changing collisions involving atoms in 1P electronic states: Ca(4s5p 1P)+noble gases

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Abstract
We present a detailed study of the mechanism of spin–changing transitions between 1P and 3P electronic states corresponding to the nsn’p Rydberg state of an alkaline earth atom in collision with a structureless, spherical partner. This type of process takes place on four potential curves and involves collisional coupling between the electronic angular momentum L of the electronically excited atom, the spin S of the atom in the final 3P state, and the orbital angular momentum l associated with the relative motion of the collision partners. We review the use of Hund’s case coupling schemes in describing the collision and present a careful analysis of the initial state preparation under conditions of laser excitation in a crossed beam experiment. This underlies the development of a new statistical model for the dependence of the spin–changing cross section on the alignment of the pump laser. Finally, we describe a new technique to follow the redistribution of flux onto locally adiabatic states as the initially excited atom is approached by the closed‐shell partner. This is used to show that dynamical corrections to our simple statistical model are small.