Wavelength Dependence of the Quenching of Iodine Fluorescence

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Abstract
The variation of the quenching efficiency of various gases (He, Xe, NO, CO2, C2H4, C6H6, I2) with energy of excitation was measured for the iodine B→X fluorescence. The correlation of efficiency with the parameter αμ½, previously found, was confirmed over a range of vibrational states. States of v′≤7 appear to be ``unquenchable'', and a fluorescence stabilization effect appears as a departure from the Stern—Volmer law. This is attributed to the absence of repulsive electronic states below the seventh vibrational level of I2. Anomalously large quenching cross sections are found for several species (NO, CO2); however, there is no conclusive evidence for a complex formation mechanism. Using these data, it was possible to locate approximately the repulsive states of I2 relative to the B state. The magnetic quenching rate can be computed to good accuracy from simple LCAO—MO wavefunctions, using first‐order time‐dependent perturbation theory. The collision‐induced quenching can be completely explained on the basis of a van der Waals‐type interaction.