Options
1994
Journal Article
Titel
High resolution UV spectroscopy of vibronic bands in p-difluorobenzene and p-difluorobenzene-Ar. The role of Herzberg-Teller coupling
Abstract
Rotationally resolved spectra of two bands in the S1 from S0 transition of the p-difluorobenzene molecule and its van der Waals complex with Ar have been measured by mass-selective resonance-enhanced two-photon ionization. The rotational structure of the 000 and the 27 1 0 bands in the monomer as well as in the complex differ from each other. They can be theoretically reproduced assuming a transition moment oriented along the short in-plane axis of the molecule in the case of the 000 transition and the long in-plane axis in the case of the 27 1 0 transition. Since the magnitude of the moments of inertia is changed in the complex by adding an Ar atom, complexation leads to a change of rotational structures of the same band. The analysis of the rotational structure points to Herzberg-Teller coupling by vibronic interaction with the S2 (1B(1u)) state as the mechanism responsible for the appearance of the 27 1 0 band. The rotational constants determined from a fit of the spectra yield an e ffective van der Waals distance of 3.55 (2) A.U. (1 A.U. = 10(exp -10) m) of the Ar atom from the p-difluorobenzene plane, which decreases by 0.06 A.U. on electronic excitation to the S1 state.