Crossed-beam reaction of C(3P j) with C2H2(1∑+g): Observation of tricarbon-hydride C3H

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Abstract
The reaction between ground statecarbon atoms, C(3 P j ), and acetylene, C2H2(1∑+ 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 C3(1∑+ g )+H2(1∑+ g ) channel. Forward‐convolution fitting of the results yielded a center‐of‐mass angular flux‐distribution forward scattered in respect to the carbonbeam, 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 π‐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.

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