Photoelectron-photon coincidence studies of the A$̃and B$̃excited electronic states of X-CC-CN+, X = CH3, CD3, Cl,Br, I

Fluorescence quantum yields and lifetimes of the above given cations in selected levels within their lowest excited electronic states have been measured by a photoelectron—photon coincidence technique. These data, obtained under collision-free conditions, lead to the radiative and non-radiative rate constants as a function of the internal energy. The symmetry of the A$\text{\$}\text{?}$state is ²A₁ (X = CH₃, CD₃), ²Σ⁺ (X = Cl), but ²Π (X = Br, I) and the corresponding k_r values for these two groups, 1–2 × 10⁶s^?1 and 2 × 10⁷s^?1 respectively, reflect the different nature of the transitions. Other essential features of the results are discussed.