Laser-Induced Selectivity for Dimerization Versus Polymerization of Butadiene Under Pressure

The pressure-induced chemical reaction of liquid butadiene was studied by Fouriertransform infrared spectroscopy in a diamond anvil cell. Dimerization was foundto occur above 0.7 gigapascal, giving vinylcyclohexene according to a cyclo-ad-diction reaction and only a trace amount of polybutadiene forms. By irradiating thehigh-pressure sample with a few milliwatts of the 488-nanometer argon? laser line,the dimerization was completely inhibited, and the rapid formation of pure trans-polybutadiene was observed. The use of different excitation wavelength allows usto emphasize the selectivity of the process and to identify the active role of the21Ag state in this pressure- and laser-induced chemical reaction.