Chemical dynamics of cyclopropynylidyne (c-C3H; X2B2) formation from the reaction of C(1D) with acetylene, C2H2(X 1Σg+)

The reaction between electronically excited carbon atoms, C(1D), and acetylene was studied at two average collision energies of 45 kJ mol−1 and 109 kJ mol−1 employing the crossed molecular beam technique. The time-of-flight spectra recorded at mass to charge m/e=37(C3H+) and m/e=36(C3+) show identical patterns indicating the existence of a carbon versus atomic hydrogen exchange pathway to form C3H isomer(s); no H2 elimination to the thermodynamically favorable tricarbon channel was observed. Forward-convolution fitting of our data shows that the reaction proceeds via direct stripping dynamics on the A′1 surface via an addition of the carbon atom to the π-orbital of acetylene to form a highly rovibrationally, short lived cyclopropenylidene intermediate which decomposes by atomic hydrogen emission to c-C3H(X 2B2). The dynamics of this reaction have important impact on modeling of chemical processes in atmospheres of comets approaching the perihelon as photolytically generated C(1D) atoms are present.