Knowledge Bank

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$\mathrm{3+}$ 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 $H3++CO\to H2+HCO+$ and $H3++CO\to H2+HOC+$ are studied by performing intrinsic reaction coordinate (IRC) calculations at the second-order M$\backslash o$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$\mathrm{3+}$ to CO are believed to be the collinear approach of H$\mathrm{3+}$ to CO, no high-level {\em ab initio} calculation of the full potential surface for the H$\mathrm{3+}$ 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 $H3++CO\to H2+HCO+$ and $H3++CO\to H2+HOC+$ are found to proceed via both bending and collinear approach of H$\mathrm{3+}$ 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.