Communication: highly accurate ozone formation potential and implications for kinetics

Atmospheric ozone is formed by the O + O(2) exchange reaction followed by collisional stabilization of the O(3)(?) intermediate. The dynamics of the O + O(2) reaction and to a lesser extent the O(3) stabilization depend sensitively on the underlying potential energy surface, particularly in the asymptotic region. Highly accurate Davidson corrected multi-state multi-reference configuration interaction calculations reported here reveal that the minimal energy path for the formation of O(3) from O + O(2) is a monotonically decaying function of the atom-diatom distance and contains no "reef" feature found in previous ab initio calculations. The absence of a submerged barrier leads to an exchange rate constant with the correct temperature dependence and is in better agreement with experiment, as shown by quantum scattering calculations.     

Theoretical study of vibronic perturbations in magnesium carbide

ABSTRACT

Understanding molecular systems with complex multi-configurational bonding has been of interest to both experimentalists and theoreticians for many years. High level dynamically weighted MRCI calculations were used to generate accurate potential energy curves for the triplet ground state ³Σ^?, and triplet excited states up to (4 ³Σ^?, 4 ³Π and 1 ³Δ) and quintet (1 ⁵Σ^? and 1 ⁵Π) states up to 50,000 cm^?1 above the ground state minimum. The lowest four ³Π states of magnesium mono-carbide (MgC) are strongly coupled leading to lifetimes that are shortened by pre-dissociation for most of the vibronic states. Non-adiabatic derivative couplings between the ³Π states were used to determine diabatic potential energy curves. The state mixing role of spin–orbit coupling, which is much weaker than the non-adiabatic interactions, is discussed. A coupled vibronic Hamiltonian was solved to compute and assign strongly mixed vibronic states. The results are compared and contrasted with the valence iso-electronic beryllium carbide (BeC) system whose results were published earlier [B.J. Barker, I.O. Antonov, J.M. Merritt, V.E. Bondybey, M.C. Heaven, and R. Dawes, J. Chem. Phys. 137, 214313 (2012)]. Transitions, spectroscopic constants and band origins are expected to aid experimental detection of MgC in the future.