A six dimensional quantum study for atom–triatom reactions: The H+H2O→H2+OH reaction

Theoretical Development of the Interaction-Asymptotic Region Decomposition Method for Tetratomic Reactive Scattering

An accurate and efficient time-dependent wave packet method is proposed for solving the product state-resolved reaction probabilities of the tetratomic reactive system. In this method, the entire scattering process is divided into the interaction region and multiple asymptotic regions, sharing the same spirit as the interaction-asymptotic region decomposition (IARD) approach in a triatomic reactive scattering process. The hyperspherical coordinate is adopted in the interaction region, while the corresponding Jacobi coordinate is employed in each asymptotic region. Therefore, in this IARD method, the "coordinate problem", the difficulty of expressing the wave function in the entire region using a single coordinate system, can be effectively avoided, and only a very small number of the grid points (or the basis functions) are required. For the numerical illustration, the typical tetratomic reaction H2 + OH with zero total angular momentum is calculated, and compared with other quantum wave packet methods. Our proposed IARD method for the tetratomic reactive system is much more efficient and accurate.

Differential Cross Sections for the H + H2S → H2 + SH Reaction: A Full-Dimensional State-to-State Quantum Dynamics Study

We utilized the time-dependent wave packet approach to compute the first full-dimensional (6D) state-to-state differential cross sections (DCSs) for the title reaction with the initial nonrotating H2S in the ground and the (100) and (001) vibrational excited states. It is found that the fundamental symmetric and asymmetric stretching excitations of H2S exhibit almost the same influence on the DCS, but unlike the H + H2O → H2 + OH reaction, they greatly increase the vibrational excitation of both the H2 and SH products. The hot vibrational state distributions of H2 are consistent with the prediction of product energy disposal by Polanyi's rules for an early barrier reaction. Because the incident H atom reacts strongly with both the ground and excited S-H states, the large populations of product SH(v2 = 1), which are very close to the relative reactivity of the initial S-H(v = 0) state, can still be explained by the local mode picture for H2S and the nonreacting SH bond's spectator nature.

Mode- and Bond-Selected Reaction of H with Local Mode Molecule HDS

Understanding mode- and bond-selected dynamics of elementary chemical reactions is of central importance in molecular reaction dynamics. The initial state-selected time-dependent wave packet method is employed to study the mode and bond selectivity, isotopic branching ratio, and temperature dependence of rate constants of the two-channel reaction of H with local mode molecule HDS. For the abstraction channel, fundamental excitation of the HS (DS) bond of the reactant HDS significantly enhances the H-abstraction (D-abstraction) reaction, whose efficacy is higher than the same amount of translational energy except at low energies just above the energy threshold. This is in sharp contrast to the prediction of Polanyi rules: translational energy is more efficient than vibrational energy in enhancing a reaction with an early barrier. The recent sudden vector projection model is then applied to rationalize the observed mode specificity, which, however, shows that the translational mode vector has a larger coupling with the reaction coordinate than the stretching vector of the active bond, implying a reversed relative efficacy on promoting the reaction as well. In contrast, the mode and bond specificity for the exchange channel is not as strong as for the abstraction channel due to the regulation of the shallow well along the reaction path.

Fermi resonance controlled product branching in the H + HOD reaction

Excitation of the first overtone of bending mode results in a significant enhancement in the HD + OH channel due to the 1 : 2 Fermi resonance between the fundamental OD stretch and the first overtone of the bend.

3D time-dependent wave-packet approach in hyperspherical coordinates for the H + O2 reaction on the CHIPR and DMBE IV potential energy surfaces

3D wavepacket quantum dynamics methodology ICS calculation of H + O₂ reaction on the CHIPR and DMBE IV PESs by J-shifting scheme.

State-to-state mode specificity in H + DOH(νOH = 1) → HD + OH(ν2 = 0) reaction: vibrational non-adiabaticity or local-mode excitation?

State-of-the-art full dimensional state-to-state quantum dynamics reveal a startling observation in which the DOH(ν_OH = 1) molecule reacts with a H atom to produce a vibrationless OH product. This interesting observation is attributed to a small OD excited local-mode component in the reactant wavefunction.

Insights into the bond-selective reaction of Cl + HOD(nOH) → HCl + OD

The theoretical study of the title reaction reveals strong bond selectivity, vibrational enhancement, and unique product distributions, in agreement with the experiment.

The sudden vector projection model for reactivity: mode specificity and bond selectivity made simple

CONSPECTUS: Mode specificity is defined by the differences in reactivity due to excitations in various reactant modes, while bond selectivity refers to selective bond breaking in a reaction. These phenomena not only shed light on reaction dynamics but also open the door for laser control of reactions. The existence of mode specificity and bond selectivity in a reaction indicates that not all forms of energy are equivalent in promoting the reactivity, thus defying a statistical treatment. They also allow the enhancement of reactivity and control product branching ratio. As a result, they are of central importance in chemistry. This Account discusses recent advances in our understanding of these nonstatistical phenomena. In particular, the newly proposed sudden vector projection (SVP) model and its applications are reviewed. The SVP model is based on the premise that the collision in many direct reactions is much faster than intramolecular vibrational energy redistribution in the reactants. In such a sudden limit, the coupling of a reactant mode with the reaction coordinate at the transition state, which dictates its ability to promote the reaction, is approximately quantified by the projection of the former onto the latter. The SVP model can be considered as a generalization of the venerable Polanyi's rules, which are based on the location of the barrier. The SVP model is instead based on properties of the saddle point and as a result capable of treating the translational, rotational, and multiple vibrational modes in reactions involving polyatomic reactants. In case of surface reactions, the involvement of surface atoms can also be examined. Taking advantage of microscopic reversibility, the SVP model has also been used to predict product energy disposal in reactions. This simple yet powerful rule of thumb has been successfully demonstrated in many reactions including uni- and bimolecular reactions in the gas phase and gas-surface reactions. The success of the SVP model underscores the importance of the transition state in controlling mode-specific and bond-selective chemistry.

Molecular hydrogen consumption in the human body during the inhalation of hydrogen gas

Inhaling or ingesting hydrogen (H2) gas improves oxidative stress-induced damage in animal models and humans. We previously reported that H2 was consumed throughout the human body after the ingestion of H2-rich water and that the H2 consumption rate ([Formula: see text]) was 1.0 μmol/min/m(2) body surface area. To confirm this result, we evaluated [Formula: see text]during the inhalation of low levels of H2 gas. After measuring the baseline levels of exhaled H2 during room air breathing via a one-way valve and a mouthpiece, the subject breathed low levels (160 ppm) of H2 gas mixed with purified artificial air. The H2 levels of their inspired and expired breath were measured by gas chromatography using a semiconductor sensor. [Formula: see text] was calculated using a ventilation equation derived from the inspired and expired concentrations of O2/CO2/H2, and the expired minute ventilation volume, which was measured with a respiromonitor. As a result, [Formula: see text] was found to be approximately 0.7 μmol/min/m(2)BSA, which was compatible with the findings we obtained using H2-rich water. [Formula: see text] varied markedly when pretreatment fasting to reduce colonic fermentation was not employed, i.e., when the subject's baseline breath hydrogen level was 10 ppm or greater. Our H2 inhalation method might be useful for the noninvasive monitoring of hydroxyl radical production in the human body.

Enhancing dissociative chemisorption of H2O on Cu(111) via vibrational excitation

The dissociative chemisorption of water is an important step in many heterogeneous catalytic processes. Here, the mode selectivity of this process was examined quantum mechanically on a realistic potential energy surface determined by fitting planewave density functional calculations spanning a large configuration space. The quantum dynamics of the surface reaction were characterized by a six-dimensional model including all important internal coordinates of H(2)O and its distance to the surface. It was found that excitations in all three vibrational modes are capable of enhancing reactivity more effectively than increasing translational energy, consistent with the "late" transition state in the reaction path.

MIXED QUANTUM-CLASSICAL SEMI-RIGID VIBRATING ROTOR TARGET MODEL FOR ATOM-POLYATOM REACTION: O(3P) + CH4 → CH3 + OH

In this paper, a mixed quantum-classical semi-rigid vibrating rotor target (QC-SVRT) model has been applied to study the reaction O(3P) + CH4 → CH3 + OH based on H + CH4 potential surface of Jordan and Gilbert. In this approach, the relative translational motion between atom and polyatom molecules is treated classically while the others are treated quantum mechanically. The reaction probabilities and rate constants were carried out using the QC-SVRT approach. It was found that the QC-SVRT results are in good agreement with the quantum results and the reaction threshold is correctly produced in the present calculation. The application of this QC-SVRT approach makes it more practical to extend quantum reaction dynamics calculation to larger molecules and more complex systems without incurring significant loss of important quantum effects.