THE T-1(N-PI(ASTERISK))[-S-0 LASER-INDUCED PHOSPHORESCENCE EXCITATIONSPECTRUM OF ACETALDEHYDE IN A SUPERSONIC FREE JET - TORSION AND WAGGING POTENTIALS IN THE LOWEST TRIPLET-STATE

The laser induced T-1(n pi)<--S-0 phosphorescence excitation spectrum of jet-cooled acetaldehyde has been observed for the first time with a rotating slit nozzle excitation system. The vibronic origins were fi tted to a set of levels that were obtained from a Hamiltonian that emp loyed flexible torsion-wagging large amplitude coordinates. The potent ial surface extracted from the fitting procedure yielded barriers to t orsion and inversion of 609.68 and 869.02 cm(-1), respectively. Minima in the potential-hypersurface at theta=61.7 degrees and alpha=42.2 de grees defined the equilibrium positions for the torsion and wagging co ordinates. A comparison to the corresponding S-1-state parameters show ed that the torsion barrier (in cm(-1)) does not greatly change, S-1/T -1 = 710.8/609.7, whereas the barrier height for the wagging-inversion barrier increases dramatically, 574.4/869.0. (C) 1996 American Instit ute of Physics.