Structure of the B state of cyclobutanone

Abstract

The Bâ†�X electronic transition of cyclobutanone is investigated from a theoretical point of view. CNDO/2-CI calculations indicate that the 205 nm band, previously assigned as π*â†�n′, is actually due to a π*â†�σ_ring transition. The carbonyl stretching and in-plane bending motions are studied by setting up potential energy curves from which the structural parameters of cyclobutanone in the B state are deduced approximately. From the experimental excited state vibrational intervals and the intensity distribution, the potential function governing the ring-puckering motion in the B state is found to be V′(Q)= 29.85[1.893 Q²+ 12.589 exp (–1.574 Q²)] cm^–1 where Q is the reduced coordinate describing the vibration. The height of the barrier to the planar ring conformation is 255 cm^–1.