Experimental and theoretical study on p-chlorofluorobenzene in the S0, S1 and D0 states

The geometric structures and vibration frequencies of para-chlorofluorobenzene (p-ClFPh) in the first excited state of neutral and ground state of cationic were investigated by resonance-enhanced multiphoton ionization (REMPI) and slow electron velocity-map imaging (SEVI). The infrared spectrum of S0 state and absorption spectrum for S1 ← S0 transition in p-ClFPh were also recorded. Based on the one-color resonant two-photon ionization (1C-R2PI) spectrum and two-color resonant two-photon ionization (2C-R2PI) spectrum, we measured the adiabatic excitation energy of p-ClFPh as 36302 ± 4 cm-1. In the 2C-R2PI SEVI spectra, the accurate adiabatic ionization potential (AIP) of p-ClFPh was extrapolated to be 72937 ± 8 cm?1 via a series of progressive measurements near threshold ionization region. In addition, Franck-Condon simulations were performed to help us confidently ascertain the main vibration modes in the S1 and D0 states. The wavenumber changes of vibration modes during the transition of S1 ← S0 and D0 ← S1 were discussed. Furthermore, the mixing of vibration modes both between S0 & S1 and S1 & D0 has been analyzed.