Ultraviolet absorption and cross sections of propargyl (C3H3) radicals in the 230-300 nm region

The ultraviolet absorption spectrum and cross sections of propargyl (C3H3) radicals have been, for the first time, determined in the gas phase in the spectral range of 230-300 nm. The propargyl radicals were produced from 193 nm excimer laser photolysis of C3H3Cl, 248 nm photolysis of C3H3Br and from reaction of Cl-atoms with propargyl chloride. The spectra obtained from the three systems were nearly identical. The ultraviolet spectrum for the propargyl radicals exhibits a relatively broad absorption with a maximum cross section of 1.2 x 10(-17) cm(2) molecule(-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 sections for propargyl chloride and propargyl bromide, precursors of propargyl radicals, in the spectral range of 160-230 nm.