Dynamical importance of van der Waals saddle and excited potential surface in C(1D)+D2 complex-forming reaction

Zhitao Shen,Mingkai Fu,Haitao Ma,Wensheng Bian,Chunfang Zhang,Jianwei Cao,Yanan Wu

doi:10.1038/ncomms14094

Abstract

Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions. Here we find that the weak long-range forces cause van der Waals saddles in the prototypical C(1D)+D2 complex-forming reaction that have very different dynamical effects from van der Waals wells at low collision energies. Accurate quantum dynamics calculations on our highly accurate ab initio potential energy surfaces with van der Waals saddles yield cross-sections in close agreement with crossed-beam experiments, whereas the same calculations on an earlier surface with van der Waals wells produce much smaller cross-sections at low energies. Further trajectory calculations reveal that the van der Waals saddle leads to a torsion then sideways insertion reaction mechanism, whereas the well suppresses reactivity. Quantum diffraction oscillations and sharp resonances are also predicted based on our ground- and excited-state potential energy surfaces.

Highlights

Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions
This is achieved with extensive dynamical calculations on the highly accurate ab initio potential energy surfaces (PESs) with van der Waals (vdW) saddles constructed by us, and our findings are important for acquiring a deeper understanding of complex-forming reactions
Bussery-Honvault et al.[26] have developed a global ab initio PES (called Bussery-Honvault-Honvault-Launay (BHL)) for the ~a1A0 state; later, the ab initio data are refitted with the reproducing kernel Hilbert space (RKHS) method to remove some spurious features of the BHL PES, and the modified PES is denoted as the RKHS PES27

Summary

Introduction

Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions. We find that the weak long-range forces cause van der Waals saddles in the prototypical C(1D) þ D2 complex-forming reaction that have very different dynamical effects from van der Waals wells at low collision energies. We show that the weak vdW forces in the entrance channel of the C(1D) þ D2 reaction (Fig. 1a), which is a prototypical complex-forming reaction[19,20,21,22], give rise to entrance channel vdW saddle (see below for a definition and Supplementary Table 1), which has very different dynamical effects from vdW well at low collision energies This is achieved with extensive dynamical calculations on the highly accurate ab initio potential energy surfaces (PESs) with vdW saddles constructed by us, and our findings are important for acquiring a deeper understanding of complex-forming reactions. C(1D) ~b1A00 þ H2 reaction confirm its excited-state PES may play an important role, and the only reported global ~b1A00 PES is the Bussery-Honvault-Julien-Honvault-Launay (BJHL) surface constructed by Bussery-Honvault et al in 2005 (ref. 37), but the inclusion of the contribution of the BJHL surface worsens the agreement of the theoretical results with the crossed-beam experiments[38], indicating the deficiency of the BJHL surface

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