Structural information on the S-0 and S-1 state of o-fluorophenol by hole burning and high resolution ultraviolet spectroscopy

The electronic transitions of o-fluorophenol situated at 36 799.382 cm(-1) and 36 906.710 cm(-1), denoted the A and B bands, respectively, have been i nvestigated by high resolution fluorescence excitation spectroscopy. Hole b urning studies together with the high resolution spectroscopy results show that both bands originate in the same ground state and can be fitted to the rotational constants of the cis isomer. The rotational constants for the e xcited states are found to be A'=3231.795 MHz, B'=2207.92 MHz and C'=1313.9 7 MHz for the A band and A'=3226.945 MHz, B'=2211.24 MHz and C'=1321.03 MHz for the B band. The planarity of the ground state is lost upon electronic excitation, which enhances the activity of an out-of-plane vibration. The A and B band transitions arise from excitations to respectively the zero and first overtone levels in the double-minimum potential of this out-of-plane vibration, which shows similarities to the so-called butterfly mode observ ed in other benzene derivatives. (C) 2000 American Institute of Physics. [S 0021-9606(00)00314-7].