Chemical dynamics of cyclopropynylidyne (c-C3H;(XB2)-B-2) formation from the reaction of C(D-1) with acetylene, C2H2(X (1)Sigma(+)(g))

The reaction between electronically excited carbon atoms, C(D-1), and acety lene 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-fli ght spectra recorded at mass to charge m/e = 37(C3H+) and m/e = 36(C-3(+)) show identical patterns indicating the existence of a carbon versus atomic hydrogen exchange pathway to form C3H isomer(s); no H-2 elimination to the thermodynamically favorable tricarbon channel was observed. Forward-convolu tion fitting of our data shows that the reaction proceeds via direct stripp ing dynamics on the (1)A' surface via an addition of the carbon atom to the pi -orbital of acetylene to form a highly rovibrationally, short lived cyc lopropenylidene intermediate which decomposes by atomic hydrogen emission t o c-C3H(X B-2(2)). The dynamics of this reaction have important impact on m odeling of chemical processes in atmospheres of comets approaching the peri helon as photolytically generated C(D-1) atoms are present. (C) 2001 Americ an Institute of Physics.