QCT dynamics study of OH/OD + GeH₄ reactions. The problem of water bending excitation

Using a full-dimensional analytical potential energy surface describing the OH/OD + GeH₄ hydrogen abstraction reactions (J. Espinosa-Garcia, C. Rangel and J. C. Corchado, Phys. Chem. Chem. Phys., 2016, 18, 16941), quasi-classical trajectory calculations were performed at 298 K to simulate the scarce experimental data at this temperature. This system presents wells in the entrance and exit channels, influencing product angular distribution, which is practically isotropic. Moreover, isotopic effects were not observed. It was found that the GeH₃ co-product presents little internal energy (11% of the total available energy), although not negligible, and that the water product receives the major part of the available energy, mainly in the newly formed OH bond, while the initial OH/OD reactant bond acts as a spectator mode. These results reproduce the experimental evidence, the larger discrepancy being in the water bending vibrational distribution, which is broader in the experiment. Several factors were analyzed to account for this discrepancy, and it was concluded that the zero-point energy violation per mode is the main, but not the only, cause.