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, a⁶D_J, ...) +Cl₂→MnCl*+Cl in a beam-gas configuration. The time-profiles of both Mn(a⁶S→z⁶P_J) laser-induced fluorescence and long-lived metastable Mn*(z⁸P_J→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*(a⁶D_J) processes, and one Mn(a⁶S) process, give rise to MnCl*(c⁵Σ⁺), while at least one a⁶D_J process, and perhaps the same a⁶S process, yield the red emission. All a⁶D_J 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.