A combined resonance enhanced multiphoton ionization and ab initio study of the first absorption band of 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, and hexafluorobenzene

作者：Ridley Trevor^*; Rogers David M; Lawley Kenneth P

来源：Journal of Chemical Physics, 2014, 141(15): 154310.

DOI：10.1063/1.4898079

The resonance enhanced multiphoton ionization (REMPI) spectra of jet-cooled penta- and hexafluorobenzene when excited in the region lambda(ex) = 265-253 nm of the first absorption band and observed only in the CF+ mass channel is dominated by rotational structure in the A <- X transition of CF. However, structure in the CF+ channel for lambda(ex) > 265 nm is not a continuation of this CF spectrum and is assigned to vibrational activity in two low-frequency modes of a distorted excited state of the parent molecule. The vibrational structure is assigned to the lowest pi pi* state from a comparison with the equivalent spectrum of 1,2,4,5-tetrafluorobenzene. Ab initio calculations at the CIS level of theory of the pi pi* state of the penta- and hexafluorobenzene reveal a much more distorted equilibrium geometry (C-1 symmetry) than that of 1,2,4,5-tetrafluorobenzene. Long progressions observed in the lambda(ex) > 265 nm REMPI spectra of C6HF5 and C6F6 are assigned to two very low frequency (similar to 30 and 80 cm(-1)) modes. The role of the close-lying pi pi* and pi sigma* states in determining the energy redistribution of the initially excited state by internal conversion is discussed. Both the fluorescent yield and the direct production of CF(X) are associated with transfer to the lower-lying pi sigma* state.

• 出版日期2014-10-21