State-specific production of MnCl*(‘ IR’, ‘red ’) in the reaction Mn(a6S, a6DJ)+Cl2
Abstract
Laser ablation of Mn and MnO2 targets has been employed to investigate the reactions Mn(a6S, a6DJ, ...) +Cl2→MnCl*+Cl in a beam-gas configuration. The time-profiles of both Mn(a6S→z6PJ) laser-induced fluorescence and long-lived metastable Mn*(z8PJ→a6S) emission show that the Mn atomic beam generated from the oxide target is much colder, both translationally and electronically, than that from the pure metal. The resulting IR (c5Σ+→a6Σ+) and red (possibly 5Δ→5Δ) chemiluminescence excitation functions for the two beam sources have been analysed by the multiple line-of-centres approach. This indicates that two Mn*(a6DJ) processes, and one Mn(a6S) process, give rise to MnCl*(c5Σ+), while at least one a6DJ process, and perhaps the same a6S process, yield the red emission. All a6DJ channels involve significant excess barriers and forward transition state shifts with increasing energy, suggesting that they proceed via inner ionic–covalent crossings in which the orientation of the odd d-electron plays a key role. Chemiluminescence from reaction of Mn(a6S) has high thresholds and a much lower reaction probability, reflecting the greater difficulty of electron transfer.