THEORETICAL STUDY OF THE POTENTIAL ENERGY SURFACE FOR THE REACTIONS $\rm {H_{3}^{+}+CO \rightarrow H_2+HCO^{+}}$ and $ \rm{H_{3}^{+}+CO \rightarrow H_2+HOC^{+}}$
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Date
2008
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Publisher
Ohio State University
Abstract
To provide insight regarding the stability of the interstellar ions HCO$^+$ and HOC$^+$, the geometries and frequencies of the stationary points (transition state, reactants, intermediates, and products) on the ground potential energy surface of the CO+H$_3^+$ system have been calculated using coupled-cluster theory with both single and double substitutions (CCSD). The energetics were then refined at the CCSD(T) level of coupled-cluster theory, including core-electron correlation at the complete basis set (CBS) limits. To elucidate the formation reaction and internal relaxation processes, the minimum-energy reaction paths (MEPs) for $\rm{H_{3}^{+}+CO \rightarrow H_2+HCO^{+}}$ and $\rm{H_{3}^{+}+CO \rightarrow H_2+HOC^{+}}$ are studied by performing intrinsic reaction coordinate (IRC) calculations at the second-order M$\o$ller-Plesset (MP2) level with single-point energy corrections at higher CCSD(T)/aug-cc-pVTZ levels. This provides important information regarding the dynamics and leads to our construction of a reduced-dimension potential energy surface (PES). Although the most favorable paths to form HCO$^+$ or HOC$^+$ via a proton hop from H$_3^+$ to CO are believed to be the collinear approach of H$_3^+$ to CO, no high-level {\em ab initio} calculation of the full potential surface for the H$_3^+$ plus CO system capable of elucidating the reaction dynamics had been reported. Our objective is to provide theoretical insight regarding the stability and formation dynamics of HCO$^+$ and HOC$^+$ and their molecular complexes with H$_2$. The reactions $\rm{H_{3}^{+}+CO \rightarrow H_2+HCO^{+}}$ and $\rm{H_{3}^{+}+CO \rightarrow H_2+HOC^{+}}$ are found to proceed via both bending and collinear approach of H$_3^+$ to CO. Approximating the full 9-dimensional PES by an effective 5-dimensional surface constructed from 128\,440 {\em ab initio} points calculated at the CCSD(T)/aug-cc-pVTZ level, should allow a proper description of all of these process.
Description
Author Institution: Guelph-Waterloo Centre for Graduate Work in Chemistry and; Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; Department of Chemistry, Faculty of Science; Ochanomizu University, Tokyo 112-8610, Japan