Temperature Dependences for the Reactions of O(-) and O(2)(-) with O(2)(a(1)Delta(g)) from 200 to 70
March 16th, 2008 | by admin |Temperature Dependences for the Reactions of O(-) and O(2)(-) with O(2)(a(1)Delta(g)) from 200 to 700 K.
Rate constants and product ion distributions for the O- and O2- reactions with O2(a 1Deltag) were measured as a function of temperature from 200 to 700 K. The measurements were made in a selected ion flow tube (SIFT) using a newly calibrated O2(a 1Deltag) emission detection scheme with a chemical singlet oxygen generator. The rate constant for the O2- reaction is approximately 7 x 10-10 cm3 s-1 at all temperatures, approaching the Langevin collision rate constant. Electron detachment was the only product observed with O2-. The O- reaction shows a positive temperature dependence in the rate constant from 200 to 700 K. The product branching ratios show that almost all of the products at 200 K are electron detachment, with an increasing contribution from the slightly endothermic charge-transfer channel up to 700 K, accounting for 75% of the products at that temperature. The increase in the overall rate constant can be attributed to this increase in the contribution the endothermic channel. The charge-transfer product channel rate constant follows the Arrhenius form, and the detachment product channel rate constant is essentially independent of temperature with a value of approximately 6.1 x 10-11 cm3 s-1.
Midey A, Dotan I, Viggiano AA.
Air Force Research Laboratory, Space Vehicles Directorate, 29 Randolph Road, Hanscom Air Force Base, Massachusetts 01731-3010, and Open University of Israel, 108 Ravutski Street, Raanana, Israel 43107.