One-dimensional tunneling calculations in the imaginary-frequency, rectilinear saddle-point normal mode

Abstract

We present tunneling calculations using the reaction path Hamiltonian in the zero-curvature approximation and a one-dimensional Hamiltonian in the imaginary-frequency, rectilinear normal mode of a saddle point, neglecting the vibrational angular momentum terms. This latter Hamiltonian was recently introduced and applied to the tunneling splitting in full-dimensional malonaldeyde [Y. Wang et al., J. Chem. Phys. 128, 224314 (2008)]. The results using the latter method are shown to be much more accurate than those using the former one for the ground-state tunneling splittings for H and D-transfer in malonaldehyde and for the D+H(2) reaction in three dimensions for zero total angular momentum.