Crossed-beam reaction of C[3 Pj] with C2 H2 [ 1 [ g 1 ]: Observation of tricarbon-hydride C3 H

The reaction between ground state carbon atoms, C~P j), and acetylene, C2H2~ (g ), was studied at an average collision energy of ~8.460.3! kJ mol using the crossed molecular beam technique. The product angular distribution and time-of-flight spectra of m/z537, i.e., C3H, were recorded. Only m/z537 was detected, but no signal from the thermodynamically accessible C3~ (g )1H2( (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 ~5.461.2! kJ mol, suggesting a simple C–H-bond-rupture to H1C3H. The reaction likely proceeds on the triplet surface with an entrance barrier to the C3H2–PES of ,~8.460.3! kJ mol via addition of the carbon atom to two bonding p-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. © 1995 American Institute of Physics.