Classical Trajectory-Based Tunneling Splittings:  The Hydrogen Atom Transfer in the Hydroperoxyl Anion

The hydroperoxyl anion HO2(-) is one of the simplest examples for multidimensional hydrogen-atom transfer. This is reflected in the tunneling splittings, which have been theoretically predicted to be highly selective concerning the excitation of either the O-O stretching, the O-H stretching, or the H-O-O bending vibration. Using the available quantum mechanical spectrum up to 5000 cm(-)(1), we scrutinize the performance of a recently proposed trajectory-based method to calculate tunneling splittings (Giese, K.; Ushiyama, H.; Kühn, O. Chem. Phys. Lett. 2003, 371, 681). It is found that this new method is capable of reproducing the general behavior of the tunneling splittings rather well. Furthermore, for this particular system, the error shows a systematic trend, which suggests the applicability of a scaling correction that could be based on a small number of exact splittings.