TEMPERATURE-DEPENDENT ULTRAVIOLET-ABSORPTION CROSS-SECTIONS OF PROPYLENE, METHYLACETYLENE AND VINYLACETYLENE

The temperature dependence of the UV absorption cross sections of prop ylene (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 p ropylene 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 cros s sections has been observed with decreasing temperature from 333 to 2 33 K. At the long wavelength tail of the absorption band the cross sec tions are found to decrease with decreasing temperature. The absorptio n 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 val ues, for methylacetylene, near the absorption peak are found to remain nearly independent of temperature, However, at the long wavelength si de 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 diffu se bands between around 190 and 230 nm. The cross section values at th e absorption peaks, determined at low temperatures, are significantly higher than those at higher temperatures, A sharp absorption feature a t 168.2 nm shows the most pronounced temperature effect, with an incre ase in cross section from 35.86 X 10(-18) to 63.54 X 10(-18) cm(2) for a temperature change of 333 to 223 K.