Knowledge Bank

The reaction $H2+CN\to H+HCN$ is of importance in the combustion of hydrocarbons in air. It is also a prototypical system for studies of polyatomic reaction dynamics. The reaction has a substantial entrance channel barrier ($\approx 1000cm-1$), which raises the possibility that pre-reactive $H2-CN$ van der Waals complex may be stable at low temperatures. We have recently detected $H2-CN$ in a free-jet expansion, using laser excitation of the B-X and A-X transitions. The complex feature associated with the monomer B-X 0-0 transition consisted of a single broad peak. This corresponds to direct excitation to the $H2+CN(B)$ dissociation continuum. From the onset of the continuum, the ground state well-depth is estimated to be $40cm-1$. Bands of $H2-CN$ associated with the monomer $A2\Pi -X2\Sigma +3-0$ transition were examined. Complex features associated with $A2\Pi 1/2$ were found to be homogeneously broadened by the spin-orbit predissociation process $H2-CN(A2\Pi 1/2,v=3)\to H2+CN(A2\Pi 3/2,v=3)[\Gamma =2.5\times 1011s-1]$ Excitation of the complex to the $A2\Pi 3/2$ spin-orbit component yielded rotationally resolved bands. A preliminary analysis of the rotational structure yields an $H2$ to CN separation of 3.7 {\AA}. The rotational lines are homogeneously broadened by the internal conversion predissociation process $H2-CN(A2\Pi 3/2,v=3)\to H2+CN(X,v=7)[\Gamma =1.3\times 1010s-1]$ Double resonance techniques have been used to examine the CN fragments produced by both predissociation channels. Data for $H2-CN$ and $D2-CN$ (experiments in progress) will be presented and discussed.