15min:

YALING CHEN AND MICHAEL C. HEAVEN, Department of Chemistry, Emory University, Atlanta, GA 30322.

~~~~~~~~~The reaction H₂ + CN -> 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 (~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-X²⁺ 3-0 transition were examined. Complex features associated with A²_1/2 were found to be homogeneously broadened by the spin-orbit predissociation process

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~H₂-CN(A²_1/2, v=3) -> H₂ + CN(A²_3/2, v=3)~~~~~~~~~~[\Gamma=2.5x10¹¹s^-1]

Excitation of the complex to the A²_3/2 spin-orbit component yielded rotationally resolved bands. A preliminary analysis of the rotational structure yields an H₂ to CN separation of 3.7Å. The rotational lines are homogeneously broadened by the internal conversion predissociation process

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~H₂-CN(A²_3/2, v=3) -> H₂ + CN(X, v=7) ~~~~~~~~~~[\Gamma=1.3x10¹⁰s^-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.