Temperature dependence of association reactions studied near 0 Kelvin

Abstract

Termolecular association reactions were studied at the low temperatures produced within the core of a free jet expansion. A strong inverse temperature dependence was found in the termolecular association rate coefficients for the reactions of NO⁺ with NO and N₂ and the results are compared with existing literature and theories. The atmospheric ramifications of the reaction NO⁺ + 2 N₂ are discussed. The temperature dependence of the termolecular association reaction of H⁺ + 2 H₂ is reported for the range 1.6-3 Kelvin and a temperature dependent rate coefficient for the range 1.6-300 Kelvin is reported using the current results and the available high temperature literature. Measurement of the autoneutralization lifetime of SF₆⁻* formed by the attachment of low energy (1-100 meV) electrons to cold SF₆ molecules within the core of a free jet expansion were made. The excited anions were found to exhibit a single lifetime in accordance with the s-wave scattering law and with literature values for the temperature dependence of both the electron attachment rate coefficient and excited anion lifetime. These studies provide insight into the attachment/detachment dynamics of negative ion scattering states under single collision conditions. The effect of neutral temperature on termolecular association reactions is examined for several chemical systems and discussed within the context of models which include the formation of a long-lived collision complex.