On the photodissociation of propadienylidene, l-C3H2.

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 C1 A1 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, kH > 10(8) s(-1).