Rotational band contour analysis of the 281-nm origin band of the S1- S0 system of 1,4-benzodioxan

Abstract

The rotational contour of the 281-nm origin band of the S 1 ← S 0 transition of 1,4-benzodioxan has been photographed and analyzed. It is shown to be type A, which establishes the transition as A ← A (in C 2), as expected for an o-disubstituted benzene with identical substituents. The changes in rotational constants from S 0 to S 1 have been found to be Δ A = −0.0033 cm −1, Δ B = −0.0001 cm −1, and Δ C = −0.00036 cm −1. The change in the inertial defect is small, ruling out a major change upon excitation of the conformation of the partly saturated ring, assumed to be twisted in S 0.