Diabatic Potential Energy Surfaces for the CaH ₂ System and Dynamics Studies for the Ca( ¹ S) + H ₂ Reaction

The global diabatic potential energy surfaces (PESs) related to the 1¹A' and 2¹A' states of the CaH₂ system were constructed using neural network method. The topographic features of the new diabatic PESs were discussed in detail. For the 1¹A' and 2¹A' states, two crossing points emerge in most configurations. Furthermore, the newly constructed diabatic PESs reasonably describe the nonadiabatic processes between electronic states. To elucidate the influence of nonadiabatic effects in the collision process between Ca and H₂, both adiabatic and nonadiabatic dynamical calculations for the Ca(¹S) + H₂ reaction were performed using the time-dependent wave packet method. Some dynamical properties including reaction probabilities, integral cross sections, and rate constants were reported and compared with previous theoretical results. The dynamical results indicate that in adiabatic calculations, the neglect of the effect of the Ca(¹P) + H₂ channel leads to significantly larger adiabatic results compared to nonadiabatic ones. Therefore, we conclude that nonadiabatic effects play a crucial role in the reaction process and cannot be ignored.