Picosecond IR study of the UV photo-induced decomposition of bis(naphthoyl)peroxide and of a naphthyl peroxycarbonate

Picosecond UV pump/IR probe experiments were carried out on bis(1-naphthoyl)peroxide (1) and on tert-butylperoxy-2-naphthylcarbonate (2) dissolved in CCl4. After excitation by a 308 nm pulse the formation of CO2 is measured with a time resolution of 1.8 ps via the IR-absorption of the nu(3)-mode at around 2340 cm(-1) for delay times up to 550 ps. A pronounced temporal and spectral evolution of the nu(3)-absorption band of CO2 is found which is assigned to the initial formation of vibrationally excited CO2 and subsequent vibrational cooling by energy transfer to the surrounding solvent. CO2 concentration versus time profiles are obtained from the time dependence of the integrated nu(3)-band absorbance. The data suggest that 2 decomposes in a consecutive stepwise process whereas 1 undergoes concerted bond scission leading to CO2 formation within the time resolution of the experiment.