ULTRAVIOLET-ABSORPTION AND CROSS-SECTIONS OF PROPARGYL (C3H3) RADICALS IN THE 230-300 NM REGION

The ultraviolet absorption spectrum and cross sections of propargyl (C 3H3) radicals have been, for the first time, determined in the gas pha se in the spectral range of 230-300 nm. The propargyl radicals were pr oduced from 193 nm excimer laser photolysis of C3H3Cl, 248 nm photolys is of C3H3Br and from reaction of Cl-atoms with propargyl chloride. Th e spectra obtained from the three systems were nearly identical. The u ltraviolet spectrum for the propargyl radicals exhibits a relatively b road absorption with a maximum cross section of 1.2 x 10(-17) cm(2) mo lecule(-1) at 242 nm. The electronic transitions in propargyl radical have also been calculated by ab initio quantum chemical methods at the CASSCF, CASPT2, CIS, and EOM_CCSD levels of theory and assign the new observed band to the in plane pi(b(2))<--pi(b(2)) allowed transition . In addition, we report here the absorption spectra and cross section s for propargyl chloride and propargyl bromide, precursors of propargy l radicals, in the spectral range of 160-230 nm.