15min:

ANDREW S. PETIT AND ANNE B. MCCOY, Department of Chemistry, The Ohio State University, Columbus, OH 43210.

Since its inception in 1975 by Anderson,\footnoteJ. B. Anderson, J. Chem. Phys. , \underline63, 1499 (1975). Diffusion Monte Carlo (DMC) has been successfully applied to a wide range of electronic and vibrational problems. In the latter case, it has been shown to be a powerful method for studying highly fluxional systems exhibiting large amplitude vibrational motions. We report here our recent work developing a new DMC algorithm capable of treating rotational excited states. We first develop the appropriate coordinates, nodal structures, and re-crossing corrections for this problem. Then, using H₃O⁺ and D₃O⁺ as model systems,\footnoteX. Huang, S. Carter, and J. Bowman, J. Chem. Phys. , \underline118, 5431 (2003). we show that our method can successfully describe a range of rotational states from |\!\!0,0,0\rangle to \frac1\sqrt2 (|\!\!10,10,0 \rangle + \!\!| \!\! 10,-10,0 \rangle). In particular, we examine the combined effects of rotational and zero-point vibrational motion on the geometric structure of the molecules. Finally, we find the | \!\! 10,0,0 \rangle state to be somewhat problematic but show that the problem is straightforward to identify and has a well-defined solution.