High resolution spectroscopy of the S-1<-S-0 electronic transition of 4-fluorostyrene in a molecular beam

The spectra of the 0: and 41 A42; bands in the near-ultraviolet S I - So electronic system of 4-fluorostyrene, formed in a supersonic expansion, have been recorded. The individual rotational lines in both bands were resolved and have been com- pletely assigned using a rigid asymmetric rotor Hamiltonian. Both bands were a/b hybrids with the transition moment inclined at an angle of 2 (352)" to the a principle inertial axis. The rotational constants were used to determine effective geometries for the molecule in the Sa and So states