The laser-induced fluorescence and hole-burning spectra of 9,9′-bianthryl (BA) and its 1:1 complexes with rare gas atoms, N2, and water were obtained under a free jet condition. The torsional potentials of the BA complexes in the S1 state were determined from the observed progressions of the torsional vibration with a fitting program routine including a cross-correlation estimation. In the BA–He complex, the double-minimum torsional potential which is symmetric to the perpendicular conformation of the two anthryl moieties became slightly asymmetric. In contrast, the attachment of large rare gas atoms, N2 or H2O to BA significantly affected the torsional motion due 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.
