Pathways and reduced-dimension five-dimensional potential energy surface for the reactions H3++CO→H2+HCO+ and H3++CO→H2+HOC+

Abstract

To obtain theoretical insight regarding the stability and formation dynamics of the interstellar ions HCO(+) and HOC(+), stationary points and the associated vibrational frequencies on the full nine-dimensional potential energy surface for the electronic ground state have been calculated using coupled-cluster theory with both single and double substitutions (CCSD). The energetics were refined with a higher-level coupled-cluster method CCSD(T), with core-valence electron correlation treated at the complete basis set limit. To elucidate the formation mechanism and internal relaxation processes, the reaction paths for the reactions H(3) (+)+CO-->H(2)+HCO(+) and H(3) (+)+CO-->H(2)+HOC(+) were calculated at the second-order Moller-Plesset (MP2) level, and corresponding single-point energies were obtained at the higher CCSD(T)/aug-cc-pVTZ level. Based on the analysis of the main reaction processes, a reduced-dimension five-dimensional potential energy surface for this system was constructed from 128 440 ab initio points calculated at the CCSD(T)/aug-cc-pVTZ level.

Preferential Isomer Formation Observed in H3+ + CO by Crossed Beam Imaging

“…Each pathway proceeds via an intermediate ion-dipole complex that follows dissociation to the final products. 19 The enthalpy difference between both channels amounts to 1.63 eV and is directly correlated with the difference in proton affinity of the carbon- and oxygen ends of CO. 20 Proton migration between both isomers has to overcome a potential energy barrier, which, however, is known to be substantially lowered by the presence of a neutral catalyst that possesses a higher proton affinity than the O-side of CO. 21,22 …”

“…Recent theoretical works have shown high level electronic structure calculations of the stationary points along these two reactions. 19,32 Other studies have analyzed the main forces involved in the interaction between H 3 + and CO and have computed the reaction rate of each isomer channel as a function of temperature. 18,33 These works predict a similar reaction rate for both isomer formations at conditions close to room temperature.…”

Temperature Dependence of Two Key Interstellar Reactions of H3+: O(3P) + H3+ and CO + H3+

“…24, 25 Here, we focus on a detailed analysis of the overall kinetics including a careful treatment of the different terms in the potential and the branching between the H 2 + HCO + and the H 2 + HOC + channels. Earlier theoretical work also considered this rate coefficient and branching ratio but with more limited representations of the potential.…”

“…LeRoy and co-workers have recently obtained similar results (within 1 kcal/mol for the key stationary points) with larger basis sets and including core-valence correlation but employing the CCSD rather than CCSD(T) method in the geometry optimizations. 25 The addition leads to two distinct intermediate complexes, with the chemical bonding to either the O or the C end of the CO. These two intermediates lead to separate sets of bimolecular products, H 2 + HCO + and H 2 + HOC + .…”

Ab initio molecular dynamics simulation on reaction

“…Herbst and Woon [14] calculated PESs for reactions (1) and (2) at the CCSD(T)/ccpVTZ level and rate coefficients based on phase space theory. Li et al [15] computed optimized geometries for reactions (1) and (2) using B3LYP, MP2 and CCSD levels of theory with the basis set aug-cc-pVTZ, single-point energies of stationary points at the CCSD(T)/aCV5Z level of theory, and single-point energies of transition states at the CCSD(T)/CVS(V+C) level of theory.…”