The state energy and the displacements of the potential minima of the 2Ag- state in all-trans-β-carotene as determined by fluorescence spectroscopy

The fluorescence spectrum of all-trans-beta-carotene was recorded at 170 K. The 1B(u)(+) --> 1A(g)(-) fluorescence exhibited clear vibrational structures constituting a mirror image with those of the 1B(u)(+) --> 1A(g)(-) absorption, and the deconvolution of the entire spectrum identified the 2A(g)(-)(0) --> 1A(g)(-)(0) transition at 14500 cm(-1). The displacements of the 1B(u)(+) and 2A(g)(-) potential minima along v(1) and v(2) (the C=C stretching and C-C stretching normal coordinates, respectively) were determined to be 1.2 and 0.9, and 1.6 and 1.5, respectively. Thus, much larger potential displacements in the 2A(g)(-) state than in the 1Bu(+) state have been shown. (C) 1999 Elsevier Science B.V, All rights reserved.