The S1←S0 electronic spectrum of 4-phenyl imidazole (4PI), previously studied in the gas phase by Hockridge et al. [Chem. Phys. Lett. 302 (1999) 538], has been re-examined at both low and high resolution using fluorescence excitation and isotopic substitution techniques. The data establish a planar structure in both states; a pure a-type origin band indicates that the S1 state is 1La in character. Analysis of the torsional progressions in the S1←S0 electronic spectrum of the 4PI tautomer, 5-phenyl imidazole (5PI), indicates a planar excited state but a non-planar ground state, with a twist angle between the two ring systems of ~27°and a barrier to planarity of ~90 cm-1.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Atomic and Molecular Physics, and Optics