VIBRONIC INTENSIFICATION OF $^{1}U(n\pi^{*}$) $\leftarrow$ $S_{o}$ OF $BENZALDEHYDE^{*}$

Abstract

The $^{1}U$ ($n\pi^{*}$) $\leftarrow$ $S_{o}$ absorption spectra of benzaldehyde, benzaldehyde -1-d, -4-d, and -$d_{6}$ were measured in the vapor state at $26^{\circ} C$ using a White cell with a 40 m pathlength. The assignments of vibronic bands to particular normal modes have been made. The experimental results establish that $v_{11}$ is by far the most active mode. The extent of the delocalization of the n- electrons into the benzene ring and the importance of the hydrogen modes in the $700-800 cm^{-1}$ region upon the vibronic intensification is discussed.