TY - JOUR

T1 - Potential energy surface for dissociation including spin-orbit effects

AU - Siebert, Matthew R.

AU - Aquino, Adelia J.A.

AU - De Jong, Wibe A.

AU - Granucci, Giovanni

AU - Hase, William L.

N1 - Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.

PY - 2012/10/1

Y1 - 2012/10/1

N2 - Previous experiments [J. Phys. Chem. A 116, 2833 (2012)] have studied the dissociation of 1,2-diiodoethane radical cation () and found a one-dimensional distribution of translational energy, an odd finding considering most product relative translational energy distributions are two-dimensional. The goal of this study is to obtain an accurate understanding of the potential energy surface (PES) topology for the unimolecular decomposition reaction C 2H 4I ++I. This is done through comparison of many single-reference electronic structure methods, coupled-cluster single-point (energy) calculations, and multi-reference energy calculations used to quantify spin-orbit (SO) coupling effects. We find that the structure of the reactant has a substantial effect on the role of the SO coupling on the reaction energy. Both the BHandH and MP2 theories with an ECP/6-31++G* basis set, and without SO coupling corrections, provide accurate models for the reaction energetics. MP2 theory gives an unsymmetric structure with different C-I bond lengths, resulting in a SO energy for similar to that for the product I-atom and a negligible SO correction to the reaction energy. In contrast, DFT gives a symmetric structure for, similar to that of the neutral C 2H 4I 2 parent, resulting in a substantial SO correction and increasing the reaction energy by 6.0-6.5kcalmol 1. Also, we find that, for this system, coupled-cluster single-point energy calculations are inaccurate, since a small change in geometry can lead to a large change in energy.

AB - Previous experiments [J. Phys. Chem. A 116, 2833 (2012)] have studied the dissociation of 1,2-diiodoethane radical cation () and found a one-dimensional distribution of translational energy, an odd finding considering most product relative translational energy distributions are two-dimensional. The goal of this study is to obtain an accurate understanding of the potential energy surface (PES) topology for the unimolecular decomposition reaction C 2H 4I ++I. This is done through comparison of many single-reference electronic structure methods, coupled-cluster single-point (energy) calculations, and multi-reference energy calculations used to quantify spin-orbit (SO) coupling effects. We find that the structure of the reactant has a substantial effect on the role of the SO coupling on the reaction energy. Both the BHandH and MP2 theories with an ECP/6-31++G* basis set, and without SO coupling corrections, provide accurate models for the reaction energetics. MP2 theory gives an unsymmetric structure with different C-I bond lengths, resulting in a SO energy for similar to that for the product I-atom and a negligible SO correction to the reaction energy. In contrast, DFT gives a symmetric structure for, similar to that of the neutral C 2H 4I 2 parent, resulting in a substantial SO correction and increasing the reaction energy by 6.0-6.5kcalmol 1. Also, we find that, for this system, coupled-cluster single-point energy calculations are inaccurate, since a small change in geometry can lead to a large change in energy.

KW - chemical dynamics

KW - density functional theory

KW - electronic structure theory

KW - spin-orbit coupling

KW - unimolecular dissociation

UR - http://www.scopus.com/inward/record.url?scp=84868359387&partnerID=8YFLogxK

U2 - 10.1080/00268976.2012.725137

DO - 10.1080/00268976.2012.725137

M3 - Article

AN - SCOPUS:84868359387

VL - 110

SP - 2599

EP - 2609

JO - Molecular Physics

JF - Molecular Physics

SN - 0026-8976

IS - 19-20

ER -