A coupled channel study of HN2 unimolecular decay based on a global ab initio potential surface.

In this paper values of the unimolecular decay lifetimes of several vibrational states of HN2 based on an accurate coupled channel dynamics study using a global analytical potential surface that was derived from previously reported ab initio calculations are reported. The surface was developed by fitting the N–N stretch part to a Morse function, with parameters that are represented by a two-dimensional spline function in terms of the H to N2 center of mass distance and approach angle. This surface reproduces the ab initio points with a root mean square error of 0.08 kcal/mol for energies below 20 kcal/mol. Modifications to the potential that describe the effect of improving the basis set in the ab initio calculations are also provided. Converged coupled channel calculations have been done for the ground rotational state of HN2 to determine lifetimes of the lowest ten vibrational states. We find that only the ground vibrational state (000) and first excited bend (001) have lifetimes longer than 1 ps. The best estimates of the lifetimes of these states are 3×10-9 and 2×10-10 s, respectively. Variation of these results with quality of the ab initio calculations is less than or equal to a factor of 5. [ABSTRACT FROM AUTHOR]