Determination of charge, atom, momentum and energy transfer rate coefficients near 5 K.

Abstract

This dissertation presents the results of several investigations into nonadiabatic reaction dynamics in the 0.5 to 10 K temperature regime. The free jet flow reactor technique for production of very low local temperatures and the method for extraction of reaction rate coefficients in this unique environment is reviewed. Ion-neutral reactions which exhibit nonadiabatic behavior are initiated by state selective resonantly enhanced multiphoton ionization and the reactions are subsequently studied using time of flight mass spectrometric detection. The importance of long lived collision complexes in nonadiabatic ion-neutral reactions is reemphasized. Collisional electronic spin orbit relaxation of Xe⁺(²P(½) is shown to be very inefficient for a wide variety of collision partners. A sequential two electron charge transfer mechanism is proposed to account for the high efficiency of the fine structure relaxation by methane and nitrous oxide both of which have open charge transfer channels. The results of fine structure state specific reactions of Ar⁺(²P(J)) with H₂, D₂, HD, CH₄ and CD₄ are presented as examples of nonadiabatic atom and electron transfer reactions. Preliminary results on vibrational-rotational relaxation of neutrals in the free jet at very low temperatures using a pump-probe technique are presented.