THE TORSION-INVERSION-BENDING ENERGY-LEVELS IN THE S-1(N, PI(ASTERISK)) ELECTRONIC-STATE OF ACETALDEHYDE - A HIGH-RESOLUTION STUDY OF THE BANDS NUMBER-7 TO NUMBER-20 IN THE JET-COOLED FLUORESCENCE EXCITATION SPECTRUM

The band assignments and analyses of the jet-cooled high-resolution la ser-induced fluorescence excitation spectrum of acetaldehyde that resu lts from the S-1(n, pi) electronic state have been extended to +600 c m(-1) from the 0(0)(0) system origin. The new assignments start at Ban d #7 and finish at Band #21. Bands #8 and #9, originally assigned to 1 4(0)(2), have now been assigned to 15(0)(3) The assignments of the low er energy bands remain unaltered, The origins of the bands that involv e the torsional modes upsilon(15) (upsilon = 1 to 4) in combination wi th the wagging mode upsilon(14) (upsilon = 1 and 2) and the upsilon(10 ) (upsilon = -1) were determined by analyses with a rigid rotational H amiltonian, These origins were fitted to a set of levels that were der ived from a torsion-wagging-bending Hamiltonian that employed flexible large amplitude coordinates. The resulting potential surface was foun d to have barriers to torsion and inversion of 712.5 and 638.6 cm, res pectively, with minima in the potential hypersurface at theta = 59.99 and alpha = 33.50 for the torsion and wagging coordinates. (C) 1998 Ac ademic Press.