Temperature dependent ultraviolet absorption cross sections of propylene, methylacetylene and vinylacetylene Original Research Article

The temperature dependence of the UV absorption cross sections of propylene (CH3CHCH2) and methylacetylene (CH3CCH) from 160 to 200 nm and vinylacetylene (CH2CHCCH) from 160 to 240 nm have been measured in the gas phase, for temperatures ranging from about 220 to 330 K. The propylene spectrum, exhibits a broad absorption band with a maximum at 172.0 nm with some structure to the short wavelength side of the broad band. At the absorption peaks a small increase (about 5%) in the cross sections has been observed with decreasing temperature from 333 to 233 K. At the long wavelength tail of the absorption band the cross sections are found to decrease with decreasing temperature. The absorption spectrum of methylacetylene in the region of 160 to 200 nm consists of a broad continuum with a maximum at 172.4 nm. The cross section values, for methylacetylene, near the absorption peak are found to remain nearly independent of temperature. However, at the long wavelength side of the absorption band the cross sections increase with increasing temperature. The spectrum of vinylacetylene consists of a very strong and structured absorption in the 160 to 170 nm region and strong diffuse bands between around 190 and 230 nm. The cross section values at the absorption peaks, determined at low temperatures, are significantly higher than those at higher temperatures. A sharp absorption feature at 168.2 nm shows the most pronounced temperature effect, with an increase in cross section from 35.86 × 10−18 to 63.54 × 10−18 cm2 for a temperature change of 333 to 223 K.