On the photodissociation of propadienylidene, l-C3H2

Abstract

We investigate the photochemistry and photodissociation dynamics of the linear C₃H₂ isomer propadienylidene by two-colour photofragment Doppler spectroscopy at excitation wavelengths between 260 and 230 nm, corresponding to excitation into the C ¹A₁ state. Propadienylidene is generated by pyrolysis from IC₃H₂Br. Almost complete conversion of the precursor can only be achieved at high pyrolysis temperatures. Two reaction channels, H-atom loss and loss of H₂ molecules, are energetically close. Our results show that H-atom loss is indeed important in the investigated energy range. The Doppler profiles indicate that 34–37% of the excess energy is released as translation. The rates for H-atom loss are faster than the time resolution of our nanosecond-laser setup, k_H > 10⁸ s⁻¹.