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

The pressure-induced chemical reaction of liquid butadiene was studied by Fourier transform infrared spectroscopy in a diamond anvil cell. Dimerization was found to occur above 0.7 gigapascal, giving vinylcyclohexene according to a cyclo-ad- diction reaction and only a trace amount of polybutadiene forms. By irradiating the high-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 us to emphasize the selectivity of the process and to identify the active role of the 21Ag state in this pressure- and laser-induced chemical reaction.