Randomization and isomerization rate constants for isocyanogen

Abstract

Classical trajectory calculations have been performed on the isomerization of isocyanogen to cyanogen using an ab initio MP2/6-311G* potential-energy surface. By running two parallel sets of calculations at each value of the energy, one in which the trajectories were started with the atoms in a standard configuration but having random momenta, and the other in which they were started with the atoms in random positions but having no momenta, it is possible to deduce both the randomization and the isomerization rates. The randomization rates are directly proportional to the density of states at the energies concerned, i.e., analogous to the Fermi's ‘golden rule’ normally applied to continuum state mixing. The isomerization rate, after allowance for the exclusion of zero-point energy pooling, is approximately one-third of the transition-state rate, calculated with the same potential-energy parameters, over the temperature range 400–600 K.