Reaction kinetics of muonium with the halogen gases (F2, Cl2, and Br2)

Quantum Wave Packet Study of the H + Br2 → HBr + Br Reaction on a New Ab Initio Potential Energy Surface

An accurate global potential energy surface (PES) for the HBr₂ system has been constructed using the fundamental invariant neural network fitting method based upon 11 698 ab initio energies at the UCCSD(T)/CBS level of theory, with the spin-orbit coupling of the ²P_3/2 orbit of the Br atom properly included. The time-dependent wave packet calculations have been performed to study the H + Br₂ → HBr + Br reaction on the new PES. The total reaction probabilities for total angular momentum J = 0 for the ground initial state show no threshold due to the submerged barrier height (-0.351 kcal/mol) of the PES. The total integral cross sections (ICS) for reactant Br₂ in ro-vibrational states (v₀ = 0, j₀ = 0, 10, 20, 30; v₀ = 1-5, j₀ = 0) were calculated for collision energy of up to 0.5 eV. It is found that the initial rotational excitation has a negligible effect on the ICS, and the initial vibrational excitation depresses the reactivity to some extent. The thermal rate constants for the title reaction in the temperature range of 100-1000 K were calculated from the Boltzmann averaging of the v₀ = 0-5 rate constants, which overestimated the experimental results to some extent.

Large Anharmonic Effects on Tunneling and Kinetics: Reaction of Propane with Muonium

Calculations of kinetic isotope effects (KIEs) provide challenging tests of quantal mass effects on reaction rates, and muonium KIEs are the most challenging. Here, we show that it can be very important to include reaction-coordinate-dependent vibrational anharmonicity along the whole reaction path to calculate tunneling probabilities and KIEs. For the reaction of propane with Mu, this decreases both the height and width of the vibrationally adiabatic potential barrier, with both effects increasing the rate constants. Our results agree well with the experimental observations.

Rate constants and kinetic isotope effects for H-atom abstraction reactions by muonium in the Mu + propane and Mu + n-butane reactions from 300 K to 435 K: challenges for theory

This paper reports measurements of the temperature dependence of the rate constants for H-atom abstraction reactions from propane and n-butane by the light isotopic H-atom muonium (Mu), k_Mu(T), over temperatures in the range 300 K to 435 K.

"Vibrational bonding": a new type of chemical bond is discovered

A long-sought but elusive new type of chemical bond, occurring on a minimum-free, purely repulsive potential energy surface, has recently been convincingly shown to be possible on the basis of high-level quantum-chemical calculations. This type of bond, termed a vibrational bond, forms because the total energy, including the dynamical energy of the nuclei, is lower than the total energy of the dissociated products, including their vibrational zero-point energy. For this to be the case, the ZPE of the product molecule must be very high, which is ensured by replacing a conventional hydrogen atom with its light isotope muonium (Mu, mass = 1/9 u) in the system Br-H-Br, a natural transition state in the reaction between Br and HBr. A paramagnetic species observed in the reaction Mu +Br2 has been proposed as a first experimental sighting of this species, but definitive identification remains challenging.