Laser-initiated chain reactions and microexplosions in solid solutions of simple alkenes and chlorine

Solid-state photochlorination reactions of ethene and propene have been initiated by pulsed ultraviolet laser photolysis. Quantum yields and product branching ratios have been determined by Fourier transform infrared spectroscopy. At 48 K, the photochemical quantum yield for the ethene/Cl₂ system is 116 ± 15. The reaction forms predominantly the anti conformer of 1,2-dichloroethane. At 50 K, the propene/Cl₂ system yields the largest quantum yields reported to date in the solid state, 740 ± 120; the anti conformer of 1,2-dichloropropane is the predominant product in this case. At 10 K, the reactions of both systems are characterized by a sudden burst of reactivity (a microexplosion) after exposure to a cumulative laser fluence of only 0.9 mJ/cm² at 337 nm. As much as 67% of the reactants are converted to products during the microexplosion. A new technique has been developed which utilizes microexplosions for determining relative IR band intensities for conformational isomers in the solid state.