CHEMILUMINESCENCE IN THE REACTION OF MN ATOMS WITH CF4

Translational excitation functions have been determined for production of several MnF states-b(5) Pi, c(5) Sigma(+), d(5) Pi, and (most pro bably) e(5) Sigma(+)-in the reaction of a laser-ablated beam of Mn ato ms with gaseous CF4. Although all observed channels show high initial thresholds, similar to 200-300 kJ mol(-1), reaction appears to be due to excited Mn atoms rather than the ground state, a(6)S. The reagent s pecies appears to be either the first or third metastable level, a(6)D (J) or a(4)D(J). Analysis of the energy dependences, in terms of a mul tiple line-of-centers model [Levy, Res. Chern. Kinet. 1993, I, 163], i ndicates that at relatively low energies, a common process is responsi ble for b(5) Pi and c(5) Sigma(+) formation, involving a similar to 14 % forward shift in reaction transition state as collision energy incre ases. Quite separate processes, without transition state shifts, lead to production of MnF(d(5) Pi) and of MnF*(e(5) Sigma(+))/''blue'' emi ssion at relatively low energies and to enhanced c(5) Sigma(+) product ion at high energies. It is possible that enhanced production of MnF( e(5) Sigma(+)) and perhaps the d(5) Pi state from similar to 650-700 k J mol(-1) derives from the depletion of MnF(b(5) Pi, c(5) Sigma(+)). Despite the undoubted negative CF4 electron affinity, it seems likely that avoided ionic-covalent curve crossings at least play a role in th e b(5) Pi/c(5) Sigma(+) production channel.