The pyrolyses of benzene and ethyl benzene in a nitrogen carrier in a static system were investigated. Some high temperature/low residence time experiments were also performed with benzene in a flow system. Product analysis was by gas chromatography,. Between 913 and 1053K benzene pyrolyses by a free radical chain mechanism. Hydrogen and diphenyl are the major products. The rate expression /2 dtH2)]/dt = 109'83 exp (-27,100/T) [C6H j mole litre sec applies between 952 and 1030K and may be explained by a simple five-step mechanism. At lower temperatures, the experimental activa- Lion energy is lower than that predicted by theory. Above 1053K, the benzene ring opens and acetylene, ethylene, methane and solid carbon are produced. Many polynuclear hydrocarbons were found to be adsorbed on the carbon and their presence suggests a-mechanism for carbon formation. Pyrolysis of ethyl benzene gives hydrogen and styrene as the major products together with methane, toluene, ethylene, ethane and benzene plus traces of higher molecular weight hydrocarbons. The pyrolysis is a chain reaction with a chain length of the order of 10 initiated by C6H5C2H5 = C6HSCH2 + CH3 for which k- 14.4 exp (-35,300/T) sec-1. This agrees well with previous work involving toluene and aniline carriers. The results may be explained by a complex mechanism involving free radicals, CH3, C6H5CH2, C6H5CHCH3, C6H5CH2CH2, C2H5, C6H5 and H. Termination seems to occur mainly by the disproportionation reaction : 2C6H5 CHCH3 = C6H5CH: CH2 + C6NSCZH5 For the reaction: C6H5CHCH3 = C6H5CH: CIi2 +H a rate constant: ka 1015.9 exp (-26,200/T) sec-1 was deduced.

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Experimental work into the molecular dynamics of excited state benzene and the development of a new ultraviolet pulse shaper are presented. The non adiabatic non radiative decay process of benzene in its first excited has been determined using pump probe time resolved photoelectron spectroscopy. An ultrafast oscillation has been found at the onset of the channel 3 region which is attributed to intersystem crossing. Our experimental findings contribute to theoretical observations of a higher than previously expected spin orbit coupling in organic polyatomic molecules. The concluding mechanism is mediated by a doorway state and is supported by quantum dynamics simulations. A pulse shaping capability has been developed to shape the output of a commercial optical parametric amplifier in the visible region using a reflective mode, folded, pulse shaping assembly employing a spatial light modulator. Second harmonic generation is used to frequency double the shaped visible pulse down to the deep ultraviolet energy region. A variety of pulse shapes have been synthesised and characterised using cross-correlation frequency resolved optical gating. The pulse shaping set-up benefits from wavelength tuneability allowing for its application to a range of coherent control schemes.

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