Negative ion–molecule reactions of ozone and their implications on the thermochemistry of O3−

Abstract

An in-line double mass spectrometer has been employed to determine reaction rate coefficients and excitation functions for several types of negative ion reactions involving ozone. The interactions studied include electron transfer reactions, such as, M−+O3→M+O3− (where M−=O−, OH−, F−, Cl−, Br−, I−, S−, SH−, Cl−2, C2H−, NO2−, and CO3−) and particle transfer reactions, such as MO−+O2→M+O3− (where MO−=O2−, NO2−, NO3−, CO3−). Translational energy thresholds have been determined for those reactions which are endothermic by applying exact Doppler corrections for the thermal motion of the neutral as well as corrections for the translational energy distribution of the projecticle ions. These experiments place a lower limit of 2.26+0.04−0.06 eV on the electron affinity of ozone. This value is in excellent agreement with the value computed from the bond dissociation energy of O3− in its most stable configuration, D00(O−–O2) =1.80 eV, as deduced from measurements of the translational energy thresholds for the collisional dissociation process, O−3+M→O−+O2+M, where M=He, Ar. Further implications of these experiments with respect to the structure, thermochemistry, and excited states of O−3 are discussed.