Yohann Scribano

The dynamics of the T + ³ HeT ⁺ ( v = 0, j = 0) → T ₂ ⁺ + ³ He reaction has been theoretically investigated by means of quantum, statistical and quasi-classical methods on a recently refined potential energy surface.

The reaction dynamics for the H + HeH⁺ → He + H₂ ⁺ reaction in its electronic ground state is investigated using two different representations of the potential energy surface (PES). The first uses a combined kernel and neural network representation of UCCSD­(T) reference data whereas the second is a corrected PES (cR-PES) that eliminates an artificial barrier in the entrance channel appearing in its initial expansion based on full configuration interaction reference data. Despite the differences between the two PESs, both yield k _v=0,j=0 ≈ 2 × 10^–9 cm³/molecule/s at T = 10 K which is consistent with a T-independent Langevin rate k _L = 2.1 × 10^–9 cm³/molecule/s but considerably larger than the only experimentally reported value k _ICR = (9.1 ± 2.5) × 10^–10 cm³/molecule/s from ion cyclotron resonance experiments. Similarly, branching ratios for the reaction outcomes are comparable for the two PESs. However, when analyzing less averaged properties such as initial state-selected T-dependent rate coefficients and final vibrational states of the H₂ ⁺ product for low temperatures, the differences in the two PESs manifest themselves in the observables. Thus, depending on the property analyzed, accurate and globally valid representations of the PES are required, whereas more approximate and empirical construction schemes can be followed for state-averaged observables.

While the growing realization of the importance of long-range interactions is being demonstrated in cold and ultracold bimolecular collision experiments, their influence on one of the most critical ion-neutral reactions has been overlooked. Here, we address the non-Langevin abrupt decrease observed earlier in the low-energy integral cross-sections and rate coefficients of the astrochemically important H + HeH+→ H2+ + He reaction. We attribute this to the presence of artificial barriers on existing potential energy surfaces (PESs). By incorporating precise long-range interaction terms, we introduce a new refined barrierless PES for the electronic ground state of HeH2+ reactive system, aligning closely with high-level ab initio electronic energies. Our findings, supported by various classical, quantum, and statistical methods, underscore the significance of long-range terms in accurately modeling reactive PESs. The low-temperature rate coefficient on this new PES shows a substantial enhancement as compared to the previous results and aligns with the Langevin behavior. This enhancement could noticeably affect the prediction of HeH+ abundance in early Universe condition.

We present a quantum dynamics method based on the propagation of interacting quan- tum trajectories to describe both adiabatic and nonadiabatic processes within the same formalism. The idea originates from the work of Poirier [Chem. Phys. 370 4–14 (2010)] and Schiff and Poirier [J. Chem. Phys. 136 031102 (2012)] on quantum dynamics with- out wavefunctions. It consists in determining the quantum force arising in the Bohmian hydrodynamic formulation of quantum dynamics using only information about quan- tum trajectories. The particular time-dependent propagation scheme proposed here results in very stable dynamics. Its performance is discussed by applying the method to analytical potentials in the adiabatic regime, and by combining it with the exact factorization method in the nonadiabatic regime.

Water and hydrogen cyanide are two of the most common species in space and the atmosphere with the ability of binding to form dimers such as H ₂ O–HCN.

We present a quantum dynamics method based on the propagation of interacting quantum trajectories to describe both adiabatic and nonadiabatic processes within the same formalism. The idea originates from the work of Poirier [Chem. Phys.2010,370, 4-14] and Schiff and Poirier [J. Chem. Phys.2012,136, 031102] on quantum dynamics without wavefunctions. It consists of determining the quantum force arising in the Bohmian hydrodynamic formulation of quantum dynamics using only information about quantum trajectories. The particular time-dependent propagation scheme proposed here results in very stable dynamics. Its performance is discussed by applying the method to analytical potentials in the adiabatic regime, and by combining it with the exact factorization method in the nonadiabatic regime.