Study of butterfly inversion of perfluoronaphthalene by laser-induced fluorescence in supersonic jet

Abstract

Fluorescence excitation and dispersed emission spectrum of jet-cooled perfluoronaphthalene is reported. The origin region of the excitation spectrum exhibits a clear progression for a very low-frequency vibration which indicates that the molecule is highly floppy in the electronic excited state. The low-frequency progression has been assigned to the butterfly inversion of the fluorine atoms perpendicular to the ring plane. Barrier height of the butterfly inversion mode for the S1 electronic state, calculated by a quadratic Gaussian-type potential function, have been found to be 14 cm^-1 only. A splitting if 7 cm^-1 between the zero-point and the first vibronic levels indicates that butterfly inversion is active even in the zero-point level of the S1 electronic state. Simulated intensity distribution pattern over the cold progression fits well with the observed spectrum. Other vibrational frequencies of both the excitation and the dispersed emission spectrum have been tentatively assigned by correlating the observed frequencies with the values obtained from Raman and IR spectrum. Analysis of the dispersed fluorescence spectrum indicates that only totally symmetric modes are active in emission.