EMISSION-SPECTROSCOPY OF THE PREDISSOCIATIVE EXCITED-STATE DYNAMICS OF ACROLEIN, ACRYLIC-ACID, AND ACRYLOYL CHLORIDE AT 199-NM

The emission spectroscopy of acrolein (C3H4O), acrylic acid (C2H3COOH) , and acryloyl chloride (C2H3COCl) excited at 199 nm elucidates the do minant electronic character of the excited state reached by the optica l transition at this wavelength. Progressions in the C=C and C=O stret ching overtones and various combination bands suggest the antibonding orbital has mixed pi()(C=C)/pi(*)(C=O) character. We interpret the re sults in conjunction with ab initio calculations at the configuration interaction singles level to identify the influence of resonance in th e excited state of these conjugated molecules. The results on acrylic acid are of particular interest as excitation in this absorption band produces the HOCO intermediate of the OH+CO-->H+CO2 reaction that is i mportant in combustion. (C) 1995 American Institute of Physics.