Time-dependent wave packet calculations for the reaction H+HCl and its isotopic reactions are carried out on the potential energy surface (PES) of Bian and Werner (BW2) [Bian, W.; Werner, H. -J., J. Chem. Phys. 2000, 112, 220]. Reaction probabilities for the exchanged and abstraction channels are calculated from various initial rotational states of the reagent. Those have then been used to estimate reaction cross sections and rate constants which also are calculated and explained by the zero-point energy and the tunneling effect. The results of this work were compared with that of previous quasiclassical trajectory calculations and reaction dynamics experiments on the abstraction channel. In addition, the calculated rate constants are in reasonably good agreement with experimental measurements for both channels. Key words: ab initio, H/D+ DCl/HCl, collision energy, integral cross section, rate constan
In order to better understand the thermal decomposition of polycyclanes, the pyrolysis of tricyclodecane has been studied in a jet-stirred reactor at temperatures from 848 to 933 K, for residence times between 0.5 and 6 s and at atmospheric pressure, in order to obtain a conversion between 0.01 and 25 %. The main products of the reaction are hydrogen, methane, ethylene, ethane, propene, 1,3-cyclopentadiene, cyclopentene, benzene, 1,5-hexadiene, toluene and 3-cyclopentyl-cyclopentene. A primary mechanism containing all the possible initiation steps, including those involving diradicals, as well…
The thermal decomposition of norbornane (dissolved in benzene) has been studied in a jet stirred reactor at temperatures between 873 and 973 K, at residence times ranging from 1 to 4 s and at atmospheric pressure, leading to conversions from 0.04 to 22.6%. 25 reaction products were identified and quantified by gas chromatography, amongst which the main ones are hydrogen, ethylene and 1,3-cyclopentadiene. A mechanism investigation of the thermal decomposition of the norbornane - benzene binary mixture has been performed. Reactions involved in the mechanism have been reviewed: unimolecular initi…
Recently, we have shown that thermal effects play a crucial role in speeding up the rate of bond-dissociation reactions. This was done by applying a simple temperature-shifted Arrhenius Law to the experimental data, corroborated with detailed account of the heat diffusion occurring within the relevant samples and identification of errors in the temperature measurements. Here, we provide three important extensions of our previous studies. First, we analyze thermal effects in reduction-oxidation (redox) reactions, where charge transfer is an integral part of the reaction. Second, we analyze not …
Artificial Thermalization in Ring-Polymer Molecular Dynamics: The Breakdown of RPMD for Gas-Phase Reactions with Pre-Reactive Complexes and How to Fix It
We apply Thermostatted Ring Polymer Molecular Dynamics (TRPMD), a recently-proposed approximate quantum dynamics method, to the computation of thermal reaction rates. Its short-time Transition-State Theory (TST) limit is identical to rigorous Quantum Transition-State Theory, and we find that its long-time limit is independent of the location of the dividing surface. TRPMD rate theory is then applied to one-dimensional model systems, the atom-diatom bimolecular reactions H+H$_2$, D+MuH and F+H$_2$, and the prototypical polyatomic reaction H+CH$_4$. Above the crossover temperature, the TRPMD rat…
Chemical reaction rates must increasingly be determined in systems that evolve under the control of external stimuli. In these systems, when a reactant population is induced to cross an energy barrier through forcing from a temporally varying external field, the transition state that the reaction must pass through during the transformation from reactant to product is no longer a fixed geometric structure, but is instead time-dependent. For a periodically forced model reaction, we develop a recrossing-free dividing surface that is attached to a transition state trajectory [T. Bartsch, R. Hernan…
At non-zero temperature and when a system has low-lying excited electronic states, the ground-state Born--Oppenheimer approximation breaks down and the low-lying electronic states are involved in any chemical process. In this work, we use a temperature-dependent effective potential for the nuclei which can accomodate the influence of an arbitrary number of electronic states in a simple way, while at the same time producing the correct Boltzmann equibrium distribution for the electronic part. With the help of this effective potential, we show that thermally-activated low-lying electronic states…
A mathematical model has been developed to simulate the kinetic and thermal behaviour of a porous solid pellet undergoing chemical reaction with a gas. The model describes the chemical reaction itself, the transfer of the gaseous species between the external gas and the pellet surface, the transport of these species to the inside of the pellet through the pores and through the layer of solid reaction products, the generation (or consumption) of heat due to the reaction and the associated heat transfer processes, together with the structural changes produced in the solid by the reaction. The mo…
Ring polymer molecular dynamics (RPMD) is an accurate method for calculating thermal chemical reaction rates. It has recently been discovered that low-temperature calculations are strongly affected by the simulation parameters. Here, for the thermally activated reaction DH + H -> D + H2, we calculate the RPMD rate constants at T = 50, 100, and 300 K and demonstrate that for T >= 100 K the standard input parameters yield accurate results, but at low temperatures (e.g., 50 K) one must increase the asymptotic distance and force constant, and decrease the umbrella integration step.
Thermal rate coefficients for the astrochemical reaction C + CH$^+$ $\to$ C$_2^+$ + H were computed in the temperature range 20-300 K by using novel rate theory based on ring polymer molecular dynamics (RPMD) on a recently published bond-order based potential energy surface and compared with previous Langevin capture model (LCM) and quasi-classical trajectory (QCT) calculations. Results show that there is a significant discrepancy between the RPMD rate coefficients and the previous theoretical results which can lead to overestimation of the rate coefficients for the title reaction by several o…
This Feature Article presents an overview of the current status of Ring Polymer Molecular Dynamics (RPMD) rate theory. We first analyze the RPMD approach and its connection to quantum transition-state theory. We then focus on its practical applications to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rate coefficients in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a…
The ring-polymer molecular dynamics (RPMD) was used to calculate the thermal rate coefficients of the two-channel roaming reaction H + MgH. Both reaction channels, tight and roaming, are explicitly considered. This is a pioneering attempt of exerting RPMD method to multi-channel reactions. With the help of a newly developed optimization-interpolation protocol for preparing the initial structures and adaptive protocol for choosing the force constants, we have successfully obtained the thermal rate coefficients. The results are consistent with those from other theoretical methods, such as variat…
Thermal feedback as a kinetic control mechanism in reaction-diffusion pattern formation
School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram（印度科学教育研究所特里凡得琅化学学院）；Center for High-Performance Computing, Indian Institute of Science Education and Research, Thiruvananthapuram（印度科学教育研究所特里凡得琅高性能计算中心）
Silver-iron carbon nitride has been obtained by pyrolysis (under inert atmosphere) of silver hexacyanoferrate(II), precipitated on graphene nanoplatelets, and examined as electrocatalyst for oxygen reduction reaction in alkaline media in comparison to silver nanoparticles and iron carbon nitride (prepared separately in a similar manner on graphene nanoplatelets). The catalytic materials have been studied in 0.1 M potassium hydroxide electrolyte using such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk electrode voltammetry. Upon application of graphene nanop…
The rate constants for recombination and exchange reactions are calculated using the flux correlation approach with a general form of the Boltzmannized flux operator, which can simultaneously describe the Kubo and traditional half-split forms. First, we consider an exactly solvable model, i.e., the free particle case, in terms of a new scaling function. Next, as a non-trivial case, we study the recombination and exchange reactions at very high pressure. Since the rate constant is calculated by Laplace transform of the flux correlation function, the result depends on how the Boltzmannized flux …
Thermal rates for the C($^3$P) + O$_2$($^3 Σ_g^-$) $\leftrightarrow$ CO($^1 Σ^+$)+ O($^1$D)/O($^3$P) reaction are investigated over a wide temperature range based on quasi classical trajectory (QCT) simulations on 3-dimensional, reactive potential energy surfaces (PESs) for the $^1$A$'$, $(2)^1$A$'$, $^1$A$''$, $^3$A$'$ and $^3$A$''$ states. The forward rate matches measurements at 15 K to 295 K whereas the equilibrium constant determined from the forward and reverse rates are consistent with those derived from statistical mechanics at high temperature. Vibrational relaxation, O+CO($ν=1, 2$) $…
Recent work has shown that in a non-thermal, multidimensional system, the trajectories in the activated complex possess different instantaneous and time-averaged reactant decay rates. Under dissipative dynamics, it is known that these trajectories, which are bound on the normally hyperbolic invariant manifold (NHIM), converge to a single trajectory over time. By subjecting these dissipative systems to thermal noise, we find fluctuations in the saddle-bound trajectories and their instantaneous decay rates. Averaging over these instantaneous rates results in the decay rate of the activated compl…
While many studies have been reported on the reactions of aliphatic hydrocarbons, the chemistry of cyclic hydrocarbons has not been explored extensively. In the present work, a theoretical study of the gas-phase unimolecular decomposition of cyclic alkyl radicals was performed by means of quantum chemical calculations at the CBS-QB3 level of theory. Energy barrier and high-pressure limit rate constants were calculated systematically. Thermochemical data were obtained from isodesmic reactions and the contribution of hindered rotors was taken into account. Classical transition state ...
The full reaction pathway between the syn-CH$_3$CHOO Criegee Intermediate via vinyl hydroxyperoxide to OH+CH$_2$COH is followed for vibrationally excited and thermally prepared reactants. The rates from vibrational excitation are consistent with those found from experiments and tunneling is not required for reactivity at all initial conditions probed. For vibrationally excited reactant, VHP accumulates and becomes a bottleneck for the reaction. The two preparations - relevant for laboratory studies and conditions in the atmosphere - lead to a difference of close to one order of magnitude in OH…
Recent experiments claimed that the enhancement of catalytic reaction rates occurs via the reduction of activation barriers driven by non-equilibrium (``hot'') electrons in plasmonic metal nanoparticles. These experiments place plasmonic photo-catalysis as a promising path for enhancing the efficiency of various chemical reactions. Here, we argue that what appears to be photo-catalysis is in fact thermo-catalysis, driven by the well-known plasmon-enhanced ability of illuminated metallic nanoparticles to serve as heat sources. Specifically, we point to some of the most important papers in the f…
The scope of this work was the determination of kinetic parameters of the thermal oxidative degradation of a Mediterranean scrub using a hybrid method developed at the laboratory. DSC and TGA were used in this study under air sweeping to record oxidative reactions. Two dominating and overlapped exothermic peaks were recorded in DSC and individualized using an experimental and numerical separation. This first stage allowed obtaining the enthalpy variation of each exothermic phenomenon. In a second time, a model free method was applied on each isolated curve to determine the apparent activation …
It has been experimentally demonstrated that reaction rates for molecules embedded in microfluidic optical cavities are altered when compared to rates observed under "ordinary" reaction conditions. However, precise mechanisms of how strong coupling of an optical cavity mode to molecular vibrations affect the reactivity and how resonance behavior emerges are still under dispute. In the present work, we approach these mechanistic issues from the perspective of a thermal model reaction, the inversion of ammonia along the umbrella mode, in presence of a single cavity mode of varying frequency and …
The kinetics and vibrational relaxation of the ${\rm N}(^4S) +{\rm O}_2(X^3Σ^-_g) \leftrightarrow {\rm O}(^3P) + {\rm NO}(X^2Π)$ reaction is investigated over a wide temperature range based on quasiclassical trajectory simulations on 3-dimensional potential energy surfaces (PESs) for the lowest three electronic states. Reference energies at the multi reference configuration interaction level are represented as a reproducing kernel and the topology of the PESs is rationalized by analyzing the CASSCF wavefunction of the relevant states. The forward rate matches one measurement at 1575 K and is s…
The rate constants for recombination and exchange processes are studied in terms of two different flux correlation approaches: one is the Yamamoto approach, which is based on the linear response theory, and the other is the Miller one. Using those approaches we consider two exactly solvable cases, i.e., the free particle and the parabolic potential models. Since the rate constants for recombination and exchange processes are calculated by Laplace transforms of the flux correlation functions, the two approaches give different results. In the present calculation, we find that the rate constant i…
In the regime of ensemble vibrational strong coupling (VSC), a macroscopic number $N$ of molecular transitions couple to each resonant cavity mode, yielding two hybrid light-matter (polariton) modes, and a reservoir of $N-1$ dark states whose chemical dynamics are essentially those of the bare molecules. This fact is seemingly in opposition to the recently reported modification of thermally activated ground electronic state reactions under VSC. Here, we provide a VSC Marcus-Levich-Jortner electron transfer model that potentially addresses this paradox: while entropy favors the transit through …
We propose a methodology for fully automated calculation of thermal rate coefficients of gas phase chemical reactions, which is based on combining the ring polymer molecular dynamics (RPMD) with the machine-learning interatomic potentials actively learning on-the-fly. Based on the original computational procedure implemented in the RPMDrate code, our methodology gradually and automatically constructs the potential energy surfaces (PESs) from scratch with the data set points being selected and accumulated during the RPMDrate simulation. Such an approach ensures that our final machine-learning m…
Learning continuous state of charge dependent thermal decomposition kinetics for Li-ion cathodes using Kolmogorov-Arnold Chemical Reaction Neural Networks (KA-CRNNs)
Department of Mechanical Engineering, Massachusetts Institute of Technology（麻省理工学院机械工程系）
The observed modification of thermal chemical rates in Fabry-Perot cavities remains a poorly understood effect theoretically. Recent breakthroughs explain some of the observations through the Grote-Hynes theory, where the cavity introduces friction with the reaction coordinate, thus reducing the transmission coefficient and the rate. The regime of rate enhancement, the observed sharp resonances at varying cavity frequencies, and the survival of these effects in the collective regime remain mostly unexplained. In this paper, we consider the \emph{cis}-\emph{trans} isomerization of HONO atomisti…
Over 85% of all chemical industry products are made using catalysts, with the overwhelming majority of these employing heterogeneous catalysts functioning at the gas-solid interface. Consequently, optimizing catalytic reactor design attracts much effort. Such optimization relies on heat transfer and fluid dynamics modeling coupled to surface reaction kinetics. The complexity of these systems demands many approximations, which can only be tested with experimental observations of quantities such as temperature, pressure, concentrations, flow rates, etc. One essential measurement is a map of the …
The temperature dependence of the thermal rate constant for the reaction Cl($^2$P) + CH$_4$ $\rightarrow$ CH$_3$ + HCl is calculated using a Gaussian Process machine learning (ML) approach to train on and predict thermal rate constants over a large temperature range. Following procedures developed in two previous reports, we use a training dataset of approximately 40 reaction/potential surface combinations, each of which is used to calculate the corresponding data base of rate constant at approximately eight temperatures. For the current application, we train on the entire dataset and then pre…
Ring polymer molecular dynamics (RPMD) has proven to be an accurate approach for calculating thermal rate coefficients of various chemical reactions. For wider application of this methodology, efficient ways to generate the underlying full-dimensional potential energy surfaces (PESs) and the corresponding energy gradients are required. Recently, we have proposed a fully automated procedure based on combining the original RPMDrate code with active learning for PES on-the-fly using moment tensor potential and successfully applied it to two representative thermally activated chemical reactions [I…
We consider a proton-transfer (PT) system described by a proton-transfer reaction (PTR) coordinate and a rate promoting vibrational (RPV) coordinate interacting with a non-Markovian heat-bath. While dynamics of PT processes has been widely discussed using two-dimensional (2D) potential energy surfaces (PES), the role of the heat-bath, in particular, for a realistic form of the system-bath interaction has not been well explored. Previous studies are largely based on one-dimensional model and linear-linear (LL) system-bath interaction. In the present study, we introduce an exponential-linear (EL…
Reaction rate theory in solids is modified taking into account intrinsic localized modes or discrete breathers (DBs) that can appear in crystals with sufficient anharmonicity resulting in violation of Arrhenius law. Large amplitude oscillations of atoms about their equilibrium positions in the lattice cause local potentials of alternating sign, which are described in terms of time-periodic modulations of the potential barriers for chemical reactions taking place in the vicinity of DBs. The reaction rate averaged over large macroscopic volumes and times including a lot of DBs is increased by a …
We present a study on ion-atom-atom reaction A+A+B$^+$ in a wide range of systems and collision energies ranging from 100$~μ$K to 10$^5~$K, analyzing the two possible products: molecules and molecular ions. The dynamics is performed via a direct three-body formalism based on a classical trajectory method in hyperspherical coordinates developed in [J. Chem. Phys. $\textbf{140}$, 044307 (2014)]. Our chief finding is that the dissociation energy of the molecular ion product acts as a threshold energy separating the low and high energy regimes. In the low energy regime, the long-range tail of the …
In the previous papers of the author it has been shown that the 1st law of thermodynamics in chemical reactions is the following one: dU=dQ+PdV+SUM In the present paper this theory was developed and it has been shown that the 1st law of thermodynamics in chemical reactions has the following form: dC=-dU+dA and -dU=dQ where dC is the change in the chemical energy, dU is the change in the internal energy. Internal energy is the energy of thermal motion of molecules.
Many catalyst devices employ flow through porous structures, which leads to a complex macroscopic mass and heat transport. To unravel the detailed dynamics of the reactive gas flow, we present an all-encompassing model, consisting of thermal lattice Boltzmann model by Kang et al., used to solve the heat and mass transport in the gas domain, coupled to a finite differences solver for the heat equation in the solid via thermal reactive boundary conditions for a consistent treatment of the reaction enthalpy. The chemical surface reactions are incorporated in a flexible fashion through flux bounda…
Using electrospray ion beam deposition, we collide the complex molecule Reichardt's Dye (C41H30NO+) at low, hyperthermal translational energy (2-50 eV) with a Cu(100) surface and image the outcome at single-molecule level by scanning tunneling microscopy. We observe bond-selective reaction induced by the translational kinetic energy. The collision impulse compresses the molecule and bends specific bonds, prompting them to react selectively. This dynamics drives the system to seek thermally inaccessible reactive pathways, since the compression timescale (sub-ps) is much shorter than the thermal…
We present an embedding technique for metallic systems that makes it possible to model energy dissipation into substrate phonons during surface chemical reactions from first principles. The separation of chemical and elastic contributions to the interaction potential provides a quantitative description of both electronic and phononic band structure. Application to the dissociation of O$_2$ at Pd(100) predicts translationally "hot" oxygen adsorbates as a consequence of the released adsorption energy (ca. 2.6 eV). This finding questions the instant thermalization of reaction enthalpies generally…
We consider a range of model potentials with metastable states undergoing molecular dynamics coupled to a thermal bath in the high friction regime, and consider how the optimal reaction coordinate depends on the diffusion anisotropy. For this we use our recently proposed method 'Spectral gap optimization of order parameters (SGOOP)' (Tiwary and Berne, Proc. Natl. Acad. Sci. 113 2839 2016). We show how available information about dynamical observables in addition to static information can be incorporated into SGOOP, which can then be used to accurately determine the 'best' reaction coordinate f…
