Dissociative electron attachment to pulsed supersonic O₂ jet : Violation of Σ⁺ \rightleftharpoons Σ^- selection rule and dependence on carrier gas proportion

2019/02/14 by Jana, Irina, Ramaprasad, Varun, Nandi, Dhananjay
#Atomic and Molecular Clusters (physics.atm-clus) #FOS: Physical sciences

paper · doi:10.48550/arxiv.1902.05279

Abstract

The formation of O^- and O₂^- ions via dissociative electron attachment to a pulsed supersonic jet of O₂ molecules containing weakly bound small van der Waals clusters seeded in a beam of argon is reported. The energy dependence of the O^- and O₂^- yield exhibits three peaks near 7, 11 and 16 eV incident electron energies. The 7 eV peak arises from the ²Π_u state of O₂^- whereas, the 11 and 16 eV peaks are ascribed to two distinct resonance states: ²Σ_g⁺ and ²Σ_u⁺ states of O₂^-, respectively, via a violation of the Σ⁺ \rightleftharpoons Σ^- selection rule. The dependence of the cross-section of these two new peaks at ∼11 and ∼16 eV on the proportion of the carrier gas is also investigated and an optimum proportion has been observed experimentally which gives the lowest temperature of 14.86 K and highest Mach number of 72.31 for the pulsed supersonic jet.

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