The role of near resonance electronic energy transfer on the collisional quenching of NO (A²Σ+) by C₆H₆ and C₆F₆ at low temperature

We present measurements of the collisional fluorescence quenching cross section of NO (A2Σ+) by benzene and hexafluorobenzene at a series of temperatures using a custom built slow flow cell and a pulsed de Laval nozzle test cell. The measurements show a deviation from the common harpoon mechanism of collisional fluorescence quenching, specifically the large quenching cross section of 147 Å2 at 300 K measured for benzene which is not predicted by the harpoon mechanism due to the low electron affinity of benzene (−1.5 eV). We speculate that the quenching of NO (A2Σ+) by benzene and hexafluorobenzene occurs through near resonance electronic energy transfer from the NO A-state to the A-state of the quencher via a pseudo-emission process. The predicted T−1/3 dependence of the cross section for this model is consistent with the experimental observations.