A. Fahr et al., ULTRAVIOLET-ABSORPTION SPECTRUM AND CROSS-SECTIONS OF VINYL (C2H3) RADICAL IN THE 225-238 NM REGION, Chemical physics, 236(1-3), 1998, pp. 43-51
The room-temperature gas-phase ultraviolet absorption spectrum and cro
ss-sections of vinyl (C2H3) radicals have been determined in the spect
ral range 225-238 nm, employing cavity ring-down absorption spectrosco
py. Vinyl radicals in these experiments were produced from the 193 nm
excimer laser photolysis of methyl vinyl ketone (CH3COC2H3) and vinyl
bromide (C2H3Br). The spectra obtained from the two systems were nearl
y identical. The observed spectrum exhibits a relatively broad and fea
tureless absorption with a cross-section of 5.3 x 10(-18) cm(2) molecu
le(-1) at 230 nm. A combined uncertainty of similar to 25% for cross-s
ection values has been assessed. The electronic transitions in the vin
yl radical have been calculated by ab initio quantum chemical methods
at the CIS, EOM-CCSD, CASSCF and CASPT2 levels of theories which assig
n the new observed band to the highly allowed and 'in plane' pi(2a ''
) <-- pi(1a '') transition. (C) 1998 Elsevier Science B.V. All rights
reserved.