Lifetime lengthening through rotational coupling: Decay in the 1B1g and 1Au states of para‐benzoquinone

The lower excitations in the B1g and Au singlet states of para‐benzoquinone correspond to the small molecule limit. Stern–Volmer type experiments in a supersonic jet have given the collision‐free lifetimes of these states. These lifetimes increase with increasing rotation, which is due to the increased (Coriolis) coupling with the background manifold. Values for the vibronic and Coriolis coupling parameters can be extracted from the data. It then becomes evident that at about 2000 cm−1 above the origin the rotational effects are masked by the singlet–triplet radiationless decay, and indeed above that energy no rotational effects are observed.