The ground state PES of the indol/indolyl pair (Figure ) exhibits strikingly similar features to that of the phenol/phenoxy pair. The ⃗ p and ⃗ q vectors have a similar angle to that of the phenol/phenoxy pair, implying that PT and ET are coupled here, too. A notable difference to the phenol/phenoxy system is the smaller separation of the ⃗ p vector from product minimun and transition state. The system thus needs much less movement along ⃗ q to reach the transition state and the product minimum. We attribute this difference to a larger degree of concertedness in the indol/indolyl pair than in phenol/phenoxy (vide infra).