Time dependence of the fluorescence of the B state of CN

Abstract

The alteration of the fluorescence of the B ²Σ state of the CN radical on collisions with foreign gases has been studied by their effect on the decay. A vacuum uv nanosecond flash lamp was used to dissociate the ICN molecule with the direct formation of the CN(B ²Σ). A value for its lifetime extrapolated to zero pressure of the parent gas is 60.8±2.0 nsec. Some gases such as He, Ar, and CF₄ do not give any measurable quenching cross section. Others such as Xe appear to quench by promoting the $B^2{\mathrm{\Sigma \; \to \; A}}^2\Pi$ radiationless transition. There is a remarkable difference between the quenching effects of N₂ and CO; a quasistable intermediate complex is proposed for the latter gas in analogy with the effect of these gases on Hg(³P₁) atoms. Many gases appear to quench by hydrogen abstraction, e.g., H₂, CH₄, C₂H₄. In its chemical properties there is a useful analogy of B ²Σ CN with the F atom. As a consequence, in hydrogen abstraction reactions, the resultant HCN is expected to be vibrationally excited as is the corresponding HF.