Tunneling rates in a two-dimensional symmetric double-well potential surface by the exterior scaling procedure

Time-independent methods which were recently developed [J. Chem. Phys. 91, 6246 (1989); 93, 3413 (1990)] to calculate tunneling rates in bound systems are applied to a two-dimensional symmetrical double-well surface proposed by Makri and Miller [J. Chem. Phys. 86, 1451 (1987)] to describe intramolecular H-atom transfer. The methods are based on exterior complex scaling either with basis-set expansions or with an iterative multichannel propagation and matching procedure. Exterior complex scaling is used to identify the initial well (characterized by an unscaled reaction coordinate) and the final well (with a complex-scaled reaction coordinate). The quantized energies of the system become complex, with imaginary parts providing the rates.