Vibronic coupling in pyrazine nπ* transitions

Vibronic coupling integrals governing the induced absorption of the first nπ* excited state have been evaluated theoretically. The calculations, based on the CNDO/S method, confirm the b_1g assignment of the 918 cm^?1 vibration, its prominent role in the intensity borrowing and its anharmonic character in the B_3u state. Furthermore they suggest that non-BO coupling and borrowing from higher electronic states cannot be neglected.