Intersystem crossing in reaction entrance channels usually arises from ‘heavy-atom’ effects. Now molecular-beam experiments show that even without heavy atoms, the O(3P) + pyridine reaction leads to spin-forbidden pyrrole + CO products. Theoretical calculations reveal efficient intersystem crossing before the entrance barrier for O-atom addition to the N-atom lone pair, which dominates reactivity at low to moderate temperatures.
- Pedro Recio
- Silvia Alessandrini
- Vincenzo Barone
