Tunneling splitting in polyatomic molecules: Application to malonaldehyde

We report an accurate and efficient full dimensional semiclassical ab initio method for calculation of energy level splitting due to tunneling in polyatomic system. The method is applied to 21-dimensional 9-atomic malonaldehyde molecule. The tunneling splittings obtained are ΔE(H)=21.2 cm−1 for hydrogen atom transfer and ΔE(D)=3.0 cm−1 for deuterium atom transfer, which are in excellent agreement with the experimental values of 21.6 cm−1 and, 2.9 cm−1 respectively. We believe that the present analysis gives the final solution to the longstanding problem.