CROSSED-BEAM REACTION OF C(P-3(J)) WITH C2H2((1)SIGMA(+)(G)) - OBSERVATION OF TRICARBON-HYDRIDE C3H

The reaction between ground state carbon atoms, C(P-3(j)), and acetylene, C2H2((1) Sigma(g)(+)), was studied at an average collision energy of (8.4+/-0.3) kJ mol(-1) using the crossed molecular beam technique. The product angular distribution and time-of-flight spectra of m/z=37, i.e., C3H, were recorded. Only m/z=37 was detected, but no signal from the thermodynamically accessible C-3((1) Sigma(g)(+))+H-2((1) Sigma(g)(+)) channel. Forward-convolution fitting of the results yielded a center-of-mass angular flux-distribution forward scattered in respect to the carbon beam, whereas the translational energy flux distribution peaked at only (5.4+/-1.2) kJ mol(-1), suggesting a simple C-H-bond-rupture to H+C3H. The reaction likely proceeds on the triplet surface with an entrance barrier to the C3H2-PES of <(8.4+/-0.3) kJ mol(-1) via addition of the carbon atom to two bonding pi-orbitals located both at C1 or at C1 and C2 of the acetylene molecule. The explicit identification of C3H product under single collision conditions strongly demands incorporation of atom-neutral reactions in reaction networks simulating chemistry in the interstellar medium, in interstellar shock waves, and in outflows of carbon stars. (C) 1995 American Institute of Physics.