A STUDY OF LOW ENERGY ELECTRON-MOLECULE AND ION-MOLECULE COLLISIONS USING RYDBERG ATOMS (IONIZATION, ASSOCIATION, ATTACHMENT, OXYGEN, WATER)
ZOLLARS, BYRON GEORGE
Doctor of Philosophy
Low energy collisions between Rydberg atoms and neutral molecules have been investigated over a wide range of principal quantum numbers n, and for several different neutral targets. The results have been used to validate the free-electron, independent particle model of Rydberg atom collisions. Comparison between theory and experiment show that at large values of n, ionization of Rb(nS,nD) Rydberg atoms in the reaction: (UNFORMATTED TABLE FOLLOWS) Rb(nS,nD) + SF(,6) (--->) Rb('+) = SF(,6)('-) (1)(TABLE ENDS) proceeds by electron transfer from the Rydberg atom to the SF(,6) molecule. The rate constants measured for this reaction are much the same as for the attachment of free, low-energy electrons to SF(,6). Thus, Rydberg collision studies can provide information about low-energy free electron interactions. Studies of the rate constants for free ion production in the reaction: (UNFORMATTED TABLE FOLLOWS) K(nD) + SF(,6) (--->) K('+) + SF(,6)('-) (2)(TABLE ENDS) showed these to decrease sharply at smaller n, falling far below the value expected on the basis of Rydberg electron attachment to SF(,6). This behavior is attributed not to breakdown of the free-electron model, but to post-attachment electrostatic interactions between the product ions, which are formed closer to each other at lower n. Model calculations that take this electrostatic interaction into account confirm this prediction. Other Rydberg atom collision processes, such as: (UNFORMATTED TABLE FOLLOWS) K(nD) + O(,2) (--->) K('+) + O(,2)('-) (3) K(nD) + H(,2)O (--->) KH(,2)O('+) + e('-) (4)(TABLE ENDS) have been studied, as they require both the Rydberg ion core and electron to participate in the collision. Since O(,2)('-) ions formed by free electron attachment have short lifetimes against autodetachment, the observation of long-lived O(,2)('-) reaction product suggests that the K('+) core ion plays a role in stabilizing the excited O(,2)('-) ions formed by Rydberg electron attachment. Stable KH(,2)O('+) ions cannot be formed in two-body K('+) - H(,2)O interactions. The detection of long-lived KH(,2)O('+) ions thus demonstrates that the Rydberg electron can play an important role in collision processes involving the core ion by serving as a third body to carry off excess energy.