The rotationally resolved electronic spectrum of p-cyanophenol

Abstract

The electronic origin transition of p-cyanophenol (4-hydroxy-benzonitrile) at 35547.46 cm⁻¹ was examined using rotationally resolved LIF spectroscopy. The experimentally determined inertial parameters are reported and compared to the results of ab initio calculations. The S₁-lifetime of p-cyanophenol is determined to be 10.6 ± 3 ns, considerably longer than the excited state lifetime of phenol (2.4 ns). This reduction of the rate of internal conversion compared to phenol is explained by different electronic coupling matrix elements for the internal conversion in phenol and p-cyanophenol. The barrier to internal rotation of the hydroxy group in the ground states is determined from the observed splitting of the rovibronic lines to 1420 ± 20 cm⁻¹. This barrier is compared to values for the ground and first excited electronic state calculated by ab initio theory.