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

The spectra of the 0(0)(0) and 41(0)(1)42(0)(1) bands in the near-ultraviolet S-1<--S-0 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 completely assigned using a rigid asymmetric rotor Hamiltonian. Both bands were a/b hybrids with the transition moment inclined at an angle of +/- (35(-5)(+4))degrees to the a principle inertial axis. The rotational constants were used to determine effective geometries for the molecule in the S-0 and S-0 states.