“…Dis sipation of some of the excitation energy before decomposition in the liquid phase may account for this, Unsaturated hydrocarbons absorb at longer wavelengths than do saturated hydrocarbons, and it is therefore not surprising that the gas phase, as well as the liquid phase, photolysis has been extensively investigated in the wavelength region 170 to 200 nm, where quartz can be used as a window material. Butenes (126,127), benzene (128), and the xylenes (129) have thus been investigated in some detail. In all cases there are pronounced effects of pressure on the primary quantum yields.…”