Structure of 4-fluorophenol and barrier to internal –OH rotation in the S1-state

Physical Chemistry Chemical Physics Pub Date: 2003-01-29 DOI: 10.1039/B210188B

Abstract

The structure and barrier to internal rotation of 4-fluorophenol in the ground state and the electronically excited S1-state has been examined by resonantly enhanced two photon ionization spectroscopy and by rotationally resolved laser induced fluorescence spectroscopy of 4-fluorophenol and 4-fluorophenol-d1. The rotationally resolved spectrum of the electronic origin of 4-fluorophenol is comprised of two subbands, which are split by 174.1?±?0.5 MHz. From the splitting, determined from the HRLIF and several torsional bands observed in the R2PI spectrum an excited state barrier for the internal rotation of the hydroxy group of 1819.0?±?5 cm?1 was calculated. The subtorsional splitting of 4-fluorophenol-d1 could not be resolved. The experimentally determined structural parameters from a fit to the rotational constants and the barrier to internal rotation in both electronic states are compared to the results of ab initio calculations. The molecule shows quinoidal distortion upon electronic excitation, with a shortening of both the C–O and the C–F bonds.

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