Formation of CH and CH from Reactions CH + CH and CH + CH.

The reactions of CH and CH radicals with CH were investigated for the first time. Reactants CH, CH, and CH were synthesized in two beams of CH diluted with helium by pulsed high-voltage discharge. We measured translational-energy distributions, angular distributions, and photoionization-efficiency spectra of CH and CH produced from the title reactions in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet photoionization. The CH (CH) + CH reaction releases 42% (33%) of available energy into the translational degrees of freedom of product CH (CH) + H and scatters products into a nearly isotropic angular distribution. The photoionization-efficiency spectrum of CH (CH) is in good agreement with that of CH (CH) produced from the CH (CH) + CH reaction. The ionization threshold, after deconvolution, was determined as 8.0 ± 0.1 eV for CH and 8.8 ± 0.1 eV for CH. The combination of measurements of product translational-energy release and photoionization-efficiency spectra indicates productions of HCH/c-HC(C)CH/c-HC(C)CH + H and HCH + H in the two title reactions, which are supported also by quantum-chemical calculations. Ratios branching to the three isomers of CH remain unknown. This work demonstrates that long carbon-chain molecules (e.g., CH and CH) can be synthesized from reactions of CH (e.g., m = 3 and 4) radicals with polyynes (e.g., HCH) and gives some valuable implications to planetary, interstellar, and combustion chemistry.