LAUSR

Abstract The structural changes of 1,2-dimethoxybenzene upon electronic excitation have been elucidated from a comparison of ab initio calculations and fits of the structural changes to experimental inertial parameters both in the basis of internal coordinates as well as in vibrational distortion coordinates. It is shown that the use of vibrational distortion coordinates leads to better agreement with the results of ab initio optimized structures compared to the use of internal coordinates in cases, that the inertial data are not sufficient for a complete structure determination. 1,2-dimethoxybenzene has been found to be only very slightly ortho-quinoidally distorted upon electronic excitation, in contrast to former expectations.