The Torsion-Inversion-Bending Energy Levels in the S1(n, pi*) Electronic State of Acetaldehyde

The band assignments and analyses of the jet-cooled high-resolution laser-induced fluorescence excitation spectrum of acetaldehyde that results from the S1(n, pi*) electronic state have been extended to +600 cm-1 from the 0(0)0 system origin. The new assignments start at Band #7 and finish at Band #21. Bands #8 and #9, originally assigned to 14(2)0, have now been assigned to 15(3)0. The assignments of the lower energy bands remain unaltered. The origins of the bands that involve the torsional modes nu15 (v = 1 to 4) in combination with the wagging mode nu14 (v = 1 and 2) and the nu10 (v = 1) were determined by analyses with a rigid rotational Hamiltonian. These origins were fitted to a set of levels that were derived from a torsion-wagging-bending Hamiltonian that employed flexible large amplitude coordinates. The resulting potential surface was found to have barriers to torsion and inversion of 712.5 and 638.6 cm-1, respectively, with minima in the potential hypersurface at theta = 59.9 degrees and alpha = 33.5 degrees for the torsion and wagging coordinates. Copyright 1998 Academic Press.