THE TORSION-INVERSION ENERGY-LEVELS IN THE S-1(N,PI-ASTERISK) ELECTRONIC-STATE OF ACETALDEHYDE FROM HIGH-RESOLUTION JET-COOLED FLUORESCENCEEXCITATION SPECTROSCOPY

The laser-induced fluorescence excitation spectrum (LIF) of acetaldehy de that results from the emission from the S-1(n, pi) electronic stat e has been observed under very high resolution with a CW pulse-amplifi ed laser under jet-cooled conditions. The origins of seven bands were determined by rotational analyses with a rigid-rotor Hamiltonian. The origins were fitted to a set of levels that were obtained from a Hamil tonian that employed flexible torsion-wagging large amplitude coordina tes. The potential surface derived from the fitting procedure yielded barriers to torsion and inversion of 721.43 and 585.13 cm(-1), respect ively. Minima in the potential hypersurface at theta = 58.6 degrees an d alpha = 35.7 degrees defined the corresponding equilibrium positions for the torsion and wagging coordinates. (C) 1996 Academic Press, Inc .