Effects of a solvent molecule on the torsional potential of 9,9 '-bianthryl

The laser-induced fluorescence and hole-burning spectra of 9,9'-bianthryl ( BA) and its 1 : 1 complexes with rare gas atoms, N-2, and water were obtain ed under a free jet condition. The torsional potentials of the BA complexes in the S-1 state were determined from the observed progressions of the tor sional vibration with a fitting program routine including a cross-correlati on estimation. In the BA-He complex, the double-minimum torsional potential which is symmetric to the perpendicular conformation of the two anthryl mo ieties became slightly asymmetric. In contrast, the attachment of large rar e gas atoms, N-2 or H2O to BA significantly affected the torsional motion d ue to its local steric repulsion, and resulted in the reduction or loss of one wing of the potential valleys of the double minimum torsional potential .