Fourier transform infrared study of the pressure and laser induced polymerization of solid acetylene

The polymerization of solid acetylene under pressure has been studied by Fo urier transform infrared (FTIR) spectroscopy. Controlled laser irradiation cycles and the employment of infrared sensors to measure the sample pressur e, allowed to separate the photochemical and the pressure effect on the inj ection and on the evolution of the reaction. The careful assignment of all the spectral features and analysis of their relative intensities and freque ncies gave evidence to the specific effect of pressure and laser irradiatio n on the reaction products. Pressure induces an ordered growth of trans-pol yenic species, while irradiation produces the opening of the double bonds a nd a consequent branching of the chains. Constant pressure measurements all owed to obtain precise information on the kinetics of the reaction. A monod imensional growth geometry, involving the molecules on the bc plane, agrees with the parameters extracted by the kinetic curves. Comparison between ex periments at different temperatures suggests an activation of the reaction essentially due to the translational lattice modes. (C) 2000 American Insti tute of Physics. [S0021-9606(00)50735-1].