Global analytical ab initio ground-state potential energy surface for the C(1D)+H2 reactive system

Abstract

A new global ab initio potential energy surface (called ZMB-a) for the 1(1)A' state of the C((1)D)+H2 reactive system has been constructed. This is based upon ab initio calculations using the internally contracted multireference configuration interaction approach with the aug-cc-pVQZ basis set, performed at about 6300 symmetry unique geometries. Accurate analytical fits are generated using many-body expansions with the permutationally invariant polynomials, except that the fit of the deep well region is taken from our previous fit. The ZMB-a surface is unique in the accurate description of the regions around conical intersections (CIs) and of van der Waals (vdW) interactions. The CIs between the 1(1)A' and 2(1)A' states cause two kinds of barriers on the ZMB-a surface: one is in the linear H-CH dissociation direction with a barrier height of 9.07 kcal/mol, which is much higher than those on the surfaces reported before; the other is in the C((1)D) collinearly attacking H2 direction with a barrier height of 12.39 kcal/mol. The ZMB-a surface basically reproduces our ab initio calculations in the vdW interaction regions, and supports a linear C-HH vdW complex in the entrance channel, and two vdW complexes in the exit channel, at linear CH-H and HC-H geometries, respectively.

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

“…A highly accurate global PES for the state of the title system was constructed based upon 6,639 symmetry unique energy points obtained from our ab initio calculations. Accurate analytical fits were generated using many-body expansions with the permutationally invariant polynomials, and the scheme of PES construction is similar to that described in our recent work35, where a highly accurate global ground-state () PES called ZMB-a was constructed. The root-mean-square error of the global fit is 0.42 kcal mol −1 for energy points below 15 kcal mol −1 relative to the C( 1 D )+D 2 asymptote, though the fitting errors in dynamically important regions are much lower.…”

“…Although there are other PESs and subsequent dynamical calculations2829, the RKHS PES is the most widely used in dynamical studies273031323334. Most recently, a highly accurate global ab initio PES (or Zhang-Ma-Bian-a (ZMB-a)) has been constructed by our group35, which is unique in the accurate description of the regions of vdW interactions and around conical intersections (CIs), and further dynamical calculations36 performed on this PES for the C( 1 D )+H 2 reaction confirm its accuracy. On the other hand, the excited-state PES may play an important role, and the only reported global PES is the Bussery-Honvault-Julien-Honvault-Launay (BJHL) surface constructed by Bussery-Honvault et al .…”

Quantum mechanical differential and integral cross sections for the C(1D) + H2(ν = 0, j = 0) → CH(ν′, j′) + H reaction

“…3 is consistent with a barrierless insertion mechanism, and the fact that the direct abstraction pathway is suppressed, since in the C( 1 D) collinearly attacking H 2 direction the ZMB-a surface shows a high barrier caused by the CI between the 1 1 A ′ and 2 1 A ′ states. 39 Almost all of the resonance peaks in the reaction probability disappear due to the partial wave summation, however, small oscillations survive. In Fig.…”

“…Since both ICSs are derived from accurate quantum dynamics calculations, the divergence should result from different topologies of the ZMB-a and RKHS PESs in the CI and long-range vdW regions, which are described better by the ZMB-a surface. 39 Figure 3 also presents the QCT ICS 40 calculated on the ZMB-a surface. As can be seen, our QM ICSs are somewhat larger than the QCT ones, and generally the agreement is quite good, except that the QM ones show small oscillations.…”

“…Although there are other ab initio-based PESs and subsequent dynamical calculations, [36][37][38] the RKHS PES is the most widely used in dynamical studies. Most recently, a highly accurate global ab initio PES (or ZMB-a) for the 1 1 A ′ state has been constructed by our group, 39 which is unique in the very good description of the regions around conical intersections (CIs) and of van der Waals (vdW) interactions. The QCT studies have been performed on the ZMB-a surface and interesting results are obtained.…”