Crossed beam reaction of the cyanogen radical, CN(X-2 Sigma(+)), with acetylene, C2H2(X-1 Sigma(+)(g)): Observation of cyanoacetylene, HCCCN(X-1 Sigma(+))

The chemical dynamics to cyanoacetylene, HCCCN(X (1)Sigma(+)), formation vi a the neutral-neutral reaction of cyanogen, CN(X (2)Sigma(+)), with acetyle ne, C2H2(X (1)Sigma(g)(+)), is investigated in a crossed molecular beams ex periment at a collision energy of 21.1 kJ mol(-1). The laboratory angular d istribution and time-of-flight spectra of the HCCCN product are recorded at m/e=51 and 50. Forward-convolution fitting of our data reveals that the re action dynamics are governed by an initial attack of the CN radical to the pi electron density of the acetylene molecule to form a HCCHCN collision co mplex on the (2)A' surface. The four heavy atoms are rotating in plane almo st perpendicular to the total angular momentum vector J around the C axis o f the complex which undergoes C-H bond rupture through a tight transition s tate to HCCCN and H. The H atom is emitted almost perpendicular to the HCCC N axis to yield a nearly "sideways" peaking of T(theta). The explicit ident ification of the cyanoacetylene reaction product represents a solid backgro und for the title reaction to be included with more confidence in reaction networks modeling the chemistry in dark, molecular clouds, outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbo n rich planets and satellites such as the Saturnian moon Titan. (C) 1999 Am erican Institute of Physics. [S0021-9606(99)02015-2].