Reactive and inelastic processes involving I2(D 1Σ+u) with the collision partners CH4, CH3Cl, CF3Cl, and CF4

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Abstract
Fluorescence from the D 1Σ+u state of I2, and from other ion‐pair states populated as a result of inelastic collisions with the molecules CH4, CH3Cl, CF3Cl, and CF4, was studied throughout the 200–510 nm region. I2(D 1Σ+u) was optically pumped using an ArF laser (λ=193 nm) and the above spectral region recorded with single laser shots by employing an optical multichannel analyzer. The physical quenching of I2(D 1Σ+u) was found to involve an electronic cascade, through intermediate states, terminating in the lowest ion‐pair state I2(3Π2g). The presence of reactive channels was identified by the reduction in I2 fluorescence following successive laser shots. Fluorescence from I2(D 1Σ+u) was also studied following excitation with a cw mercury lamp (λ=185 nm) and Stern–Volmer analysis of these data yielded total removal rate constants (reactive+inelastic channels), viz; k(CH4)=(7.9±0.3)×10−10, k(CH3Cl)=(21.0±1.0)×10−10, k(CF3Cl)=(7.1±0.4)×10−10, k(CF4)=(6.0±1.0)×10−10 (all in cm3 molecule−1 s−1 units). The presence of reactive channels was confirmed using end‐product analysis techniques and it was shown that the lowest ion‐pair state I2(3Π2g) also reacts with CH4 and possibly with CF3Cl.