High-Resolution Crossed-Beam Dynamics Studies of the D + Para-H2 → HD + H Reaction at 1.21 eV

Understanding kinetic isotope effects is important in the study of the reaction dynamics of elementary chemical reactions, particularly those involving hydrogen atoms and molecules. As one of the isotopic variants of the hydrogen exchange reaction, the D + para-H2 reaction has attracted much attention. However, experimental studies of this reaction have been limited primarily due to its strong experimental background noise. In this study, by using the velocity map ion imaging method and the near-threshold ionization technique, together with improvements on the vacuum condition in the vicinity of the collision zone, background noise was reduced significantly, and quantum state-resolved differential cross sections (DCSs) for the D + para-H2 reaction at a collision energy of 1.21 eV were acquired in a crossed molecular beams experiment. Interestingly, clear rotational state-dependent angular distributions were noticed in the quantum state-resolved DCSs. The most intense peak's positions for HD (v', j') products shift to different scattering directions as the product's ro-vibrational quantum number increases. Two different microscopic reaction mechanisms are found to be involved in this reaction for HD products in different vibrational states. The results show a direct correlation between the scattering angle and the product's rotational quantum number, revealing that the contributions of impact parameters are strongly influenced by the corresponding centrifugal barrier.

Imaging the Complex-Forming Reaction Dynamics in Al + CO2 → AlO + CO

For indirect reactions involving more than one intermediate complex from reactant valley to product valley, the reaction dynamics becomes very complicated for researchers due to competition between pathways. In order to resolve the large discrepancy between theoretical and experimental studies on the linear or bent structures of complexes involved in the title endothermic reaction, we performed a crossed-beam experiment at a large collision energy (E_c) range with mapping of the velocity distributions of Al reactants and AlO products. We found that the reaction proceeds through different complex-forming mechanisms with the increase of E_c: at low E_c near the reaction threshold, only low impact-parameter collisions contribute through a collinear Al-OCO short-lived complex, and at high E_c, the bent-structure complexes, formed by either isomerization or noncollinear collisions, come into play.

A new potential energy surface of the OH2+ system and state-to-state quantum dynamics studies of the O+ + H2 reaction

A new global potential energy surface of the O⁺ + H₂ system was constructed with neural network method, using about 63000 ab initio points, which were calculated by employing the multi-reference configuration interaction method with aug-cc-pVTZ and aug-cc-pVQZ basis sets.

SEVEN-DIMENSIONAL QUANTUM DYNAMICS STUDY OF THE H2 + NH2 → H + NH3 REACTION ON AN INTERPOLATED POTENTIAL ENERGY SURFACE

Initial-state-selected time-dependent wave packet dynamics studies have been performed for the H 2 + NH 2 → H + NH 3 reaction with a seven-dimensional model on a new interpolated ab initio potential energy surface (PES). The PES is constructed using modified Shepard interpolation Scheme and contains 1967 data points with ab initio calculations carried out on UCCSD(T)/aug-cc-pVTZ level. In the seven-dimensional model, NH 2 group keeps C2v symmetry and two NH bonds are fixed at their equilibrium values. The total reaction probabilities are calculated when (1) the two reactants are initially at their ground states; (2) NH 2 bending mode is excited, and (3) H 2 is on its first vibrational excited state. The integral cross sections are also reported for these initial states with centrifugal-sudden approximation. Thermal rate constants are calculated for the temperature range of 200–2000 K and compared with the previous calculated values and available experimental data. Good agreements between theory and experiments for the rate constants at intermediate temperature are achieved on this PES.