Abstract
A vibrationally very rich and sharp spectrum with noticeable rotational fine structure has been recorded for the lowest singlet in-plane polarized transition of 1-azaindolizine with origin at 30030.2 cm
−1. Through Franck-Condon relative intensity calculations, and a knowledge of the ground state fundamentals determined by ir measurements, a very detailed analysis of the spectrum has been achieved. Dependence of the band contours on interference between the allowed and vibronically induced intensity components has been noted. The large linewidths recorded for the second system are considered as possible evidence for the presence of a near-lying
I
nπ
∗
state.