Prediction of product branching ratios in the C(P3)+C2H2→l-C3H+H∕c-C3H+H∕C3+H2 reaction using ab initio coupled clusters calculations extrapolated to the complete basis set combined with Rice-Ramsperger-Kassel-Marcus and radiationless transition theories

Ab initio CCSD(T) calculations of intermediates and transition states on the singlet and triplet ${\mathrm{C}}_3{\mathrm{H}}_2$ potential energy surfaces extrapolated to the complete basis set limit are combined with statistical computations of energy-dependent rate constants of the $\mathrm{C}\left({}^{3}P\right)+{\mathrm{C}}_2{\mathrm{H}}_2$ reaction under crossed molecular beam conditions. Rice-Ramsperger-Kassel-Marcus theory is applied for isomerization and dissociation steps within the same multiplicity and radiationless transition and nonadiabatic transition state theories are used for singlet-triplet intersystem crossing rates. The calculated rate constants are utilized to predict product branching ratios. The results demonstrate that, in qualitative agreement with available experimental data, $c\text{-}{\mathrm{C}}_3\mathrm{H}+\mathrm{H}$ and ${\mathrm{C}}_3+{\mathrm{H}}_2$ are the most probable products at low collision energies, whereas $l\text{-}{\mathrm{C}}_3\mathrm{H}+\mathrm{H}$ becomes dominant at higher $E_c$ above $\sim 25\mathrm{kJ}∕\mathrm{mol}$ .