INVESTIGATING THE C-CL ANTIBONDING CHARACTER IN THE PI-PI-ASTERISK EXCITED-STATE OF VINYL, ALLYL, AND PROPARGYL CHLORIDE - EMISSION-SPECTRAAND AB-INITIO CALCULATIONS

We report the emission spectra of dissociating vinyl, allyl, and propa rgyl chloride upon photoexcitation at 199 nm. To provide a better unde rstanding of the mixed electronic character in the Franck-Condon regio n of the excited states accessed, we also present ab initio calculatio ns at the configuration interaction level for these three molecules. T hese experimental and theoretical results indicate large differences i n the contribution of n sigma(C-Cl) and pi sigma*(C-Cl) character to these predominantly pi pi(C=C/C=C) transitions. We present arguments based on the symmetry of the pertinent molecular orbitals to explain t his observed variation. We conclude by considering how the differing e lectronic character of the excited state in these molecules may influe nce the branching ratios to C-Cl fission and HCl elimination products observed in the photodissociation of vinyl, allyl, and propargyl chlor ide.