Position matters: high resolution spectroscopy of 6-methoxyindole.

The structures of syn and anti 6-methoxyindole have been determined in the electronic ground and excited states using rotationally resolved electronic spectroscopy and high level ab initio calculations. Second order coupled cluster theory predicts the lowest excited singlet states to be heavily mixed and the transition dipole moments to depend strongly on the geometries. From the analysis of the rovibronic spectra of seven isotopomers, the absolute orientation of the transition dipole moment within the principle axis frame was determined to be L(b)-like for both conformers.