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Title: Potential energy surfaces for the HBr{sup +} + CO{sub 2} → Br + HOCO{sup +} reaction in the HBr{sup +} {sup 2}Π{sub 3/2} and {sup 2}Π{sub 1/2} spin-orbit states

Quantum mechanical (QM) + molecular mechanics (MM) models are developed to represent potential energy surfaces (PESs) for the HBr{sup +} + CO{sub 2} → Br + HOCO{sup +} reaction with HBr{sup +} in the {sup 2}Π{sub 3/2} and {sup 2}Π{sub 1/2} spin-orbit states. The QM component is the spin-free PES and spin-orbit coupling for each state is represented by a MM-like analytic potential fit to spin-orbit electronic structure calculations. Coupled-cluster single double and perturbative triple excitation (CCSD(T)) calculations are performed to obtain “benchmark” reaction energies without spin-orbit coupling. With zero-point energies removed, the “experimental” reaction energy is 44 ± 5 meV for HBr{sup +}({sup 2}Π{sub 3/2}) + CO{sub 2} → Br({sup 2}P{sub 3/2}) + HOCO{sup +}, while the CCSD(T) value with spin-orbit effects included is 87 meV. Electronic structure calculations were performed to determine properties of the BrHOCO{sup +} reaction intermediate and [HBr⋯OCO]{sup +} van der Waals intermediate. The results of different electronic structure methods were compared with those obtained with CCSD(T), and UMP2/cc-pVTZ/PP was found to be a practical and accurate QM method to use in QM/MM direct dynamics simulations. The spin-orbit coupling calculations show that the spin-free QM PES gives a quite good representation of the shape ofmore » the PES originated by {sup 2}Π{sub 3/2}HBr{sup +}. This is also the case for the reactant region of the PES for {sup 2}Π{sub 1/2} HBr{sup +}, but spin-orbit coupling effects are important for the exit-channel region of this PES. A MM model was developed to represent these effects, which were combined with the spin-free QM PES.« less
Authors:
; ;  [1] ; ;  [2] ;  [1] ;  [3] ;  [4] ;  [5]
  1. Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409 (United States)
  2. Dipartimento di Chimica e Chimica Industriale, University of Pisa, Pisa (Italy)
  3. (United States)
  4. Department of Engineering, Swarthmore College, Swarthmore, Pennsylvania 19081 (United States)
  5. Department of Chemistry, Haverford College, Haverford, Pennsylvania 19041 (United States)
Publication Date:
OSTI Identifier:
22415500
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 10; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BENCHMARKS; CARBON DIOXIDE; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; ELECTRONIC STRUCTURE; EXCITATION; HYDROBROMIC ACID; L-S COUPLING; POTENTIAL ENERGY; POTENTIALS; QUANTUM MECHANICS; REACTION INTERMEDIATES; SURFACES; VAN DER WAALS FORCES