High-resolution electronic spectroscopy of molecular conformers. 3-Hydroxy and 3-deuteroxy benzoic acid esters

Rotationally resolved fluorescence excitation spectra of the origin bands in the S1← S0 transitions of each of the four conformers of jet-cooled methyl-3-hydroxy- and methyl-3-deuteroxybenzoate have been recorded. Analysis of the rotational structure has yielded rotational constants of both the ground and electronically excited states, their inertial defects, and the ab hybrid characters of the observed bands. Application of Kraitchmanʹs equations to the two isotopomers makes possible assignment of the pairs of conformers associated with the cis and trans configurations of the OH(D) substituent and the cis and trans configurations of the ester substituent. The analysis provides a determination of the absolute orientations of the transition moments in the molecular frame and their dependence on both the nuclear positions and electron densities of the substituents in both 3-hydroxy and 3-amino benzoic acid esters.