The goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods

Muckerman, J.T.

Yu, H.G.

Yu, H. G.

Muckerman, J. T.

UNT Digital Library

    BNL-91217-2010-CP    Gas-Phase Molecular Dynamics:  Theoretical Studies in Spectroscopy and Chemical Dynamics  Hua-Gen Yu and James T. Muckerman  Chemistry Department, Brookhaven National Laboratory, Upton, NY, USA   Presented at The Annual Combustion Research Conference Airlie Conference Center, Annapolis, MD June 1-4, 2010   March 2010      Chemistry Department  Brookhaven National Laboratory P.O. Box 5000 Upton, NY 11973-5000 www.bnl.gov        Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.   This preprint is intended for publication in a journal or proceedings.  Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.   DISCLAIMER  This report was prepared as an account of work sponsored by an agency of the United States Government.  Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors.  The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.                                    GAS-PHASE MOLECULAR DYNAMICS: THEORETICAL STUDIES IN SPECTROSCOPY AND CHEMICAL DYNAMICS Hua-Gen Yu (hgy@bnl.gov) and James T. Muckerman (muckerma@bnl.gov) Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973-5000 Program Scope The goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods. Recent Progress Kinetics and dynamics study of the reaction of HOCO radical with CH3 and ClO radicals A combined ab initio direct dynamics and RRKM (Rice-Ramsperger-Kassel-Marcus) study has been carried out for the reaction of HOCO radicals with CH3 radicals. It is examined using the coupled cluster method (CCSD(T)) to locate and optimize the critical points on the ground-state potential energy surface as shown in Fig.1. The results show that the CH3 + HOCO reaction can produce both the H2O + CH2CO and the CH4 + CO2 products through acetic acid (M1) and enediol (M2) intermediates. Direct ab initio dynamics calculations determine the thermal rate coefficients to be k(T/K) = 3.24×10-11 T 0.1024 in cm3molec-1s-1 at T ≤ 1000 K for the overall reaction. The product branching ratio of (H2O + CH2CO) to (CH4 + CO2) is predicted to be RH2O/CH4(T/K) = 1.52+(1.95×10-4)T using the RRKM approach. Both the thermal rate coefficients and the product branching ratios weakly depend on temperature. In addition, the kinetics of the ClO + HOCO reaction has been studied using the variational RRKM theory based on a CCSD(T) potential energy surface. This is a fast reaction leading to a diversity of products via an addition or direct hydrogen abstraction reaction mechanism. At room temperature, the thermal rate coefficient is obtained as 4.26×10-12 cm3molec-1s-1 with the product branching fractions of Cl (0.518), HOCl (0.469), HCl (0.01), and HClO (0.003) at zero pressure. Furthermore, a simple RRKM/master equation simulation indicates that the stabilization of the HOC(O)OCl intermediates is noticeable at moderate Figure 1. CCSD(T)/aug-cc-pVQZ energy diagram for the reaction pathway of the CH3 + HOCO reaction. BNL-91217-2010-CPpressures as its thermal rate constant reaches about 6.0×10-13 cm3molec-1s-1. This work was done in collaboration with J. Francisco (Purdue). Dynamics study of molecular ion-molecule reaction The direct molecular dynamics method was employed to study the reaction of CO with H3+ and H2D+ using a scaling all correlation second-order Mφller–Plesset perturbation theory (SAC-MP2) method with the cc-pVTZ basis set. Results show that total thermal rate coefficients for both the CO + H3+ and the CO + H2D+ reactions have a weakly positive temperature dependence. At room temperature, the rate coefficients are predicted to be (1.42 ± 0.03)×10−9 cm3molec−1s−1 with a product branching ratio of [HOC+]/[HCO+] = 0.36 ± 0.01 for the CO + H3+ reaction, and (1.26 ± 0.03)×10−9 cm3 molec−1s−1 with the product branching ratios: 0.37 ± 0.01 (([HOC+] + [DOC+])/([HCO+] + [DOC+])), 0.54 ± 0.02 ([DCO+]/[HCO+]), and 0.49±0.02 ([DOC+]/[HOC+]) for CO + H2D+. The product branching ratios have a noticeable temperature dependence as well as a pronounced isotopic effect for the H/DOC+ product channel. Spherical electron cloud hopping molecular dynamics simulation on dissociative recombination (DR) of protonated water The SECH MD method has been applied to study the DR of H3O+ at zero collision energy. The simulations give several product channels: 0.660 for (OH + 2H), 0.230 for (H2O + H), 0.108 for (OH + H2), and 0.002 for (O + H + H2), which are in excellent agreement with the heavy-ion storage ring experimental results. It was noticed that the first excited state of H3O plays a prominent role in DR of H3O+. The OH + H2 channel proceeds on this excited state and associated non-adiabatic transitions. Similar dynamics events were also observed by Lester and co-workers in their dynamics measurement of the OH (A 2Σ) + H2 collisions. In addition, two different pathways leading to hydrogen atoms are identified in the H3O+ DR processes, by analysis of the trajectories, and the bimodal distribution of released kinetic energies of hydrogen atoms. A general program for calculating vibrational spectra of five-atom systems Besides the electronic structure and molecular dynamics calculations, our research is also focuses on quantum dynamics studies of molecular spectroscopy. In this project, we aim to develop computational algorithms to accurately calculate the rovibrational spectra of polyatomic molecules, and to assist experimentalists to interpret their observed spectra. By using the two layer Lanczos iterative diagonalization algorithm developed by us previously, we have programmed an exact variational algorithm for calculating vibrational energy levels of pentatomic molecules using a rigorous quantum dynamics method. The algorithm has exploited a common compact Hamiltonian expressed in a set of four orthogonal polyspherical vectors. Since the orthogonal coordinates are a set of scattering coordinates, the large amplitude motions of vibrations and molecular dissociation events are well described. It is possible to study highly excited vibrational states and resonances (metastable vibrational states) of molecules. With the intermediate use of atomic Cartesian coordinates, any functional form can be used for expressing the potential energy surface of the system of interest. In addition, the vibrational states are efficiently solved using a two-layer Lanczos algorithm in a mixed grid/basis representation. A non-direct product basis is used in the angular variables, which avoids the singularity of the Hamiltonian at sinθ = 0. The two-layer Lanczos algorithm solves the whole eigenvalue problem in two consecutive diagonalizations in a five dimensional manner, and only requires the actions of Hamiltonian on a vector, without explicitly storing the Hamiltonian matrix. Thus, a very large basis set is allowed in calculations, which makes this work feasible. In particular, the algorithm is problem-independent so that it is universal and applicable to most penta-atomic molecules with small and/or large amplitude vibrations. A general code (PetroVib) has been programmed. The program has been successfully applied for calculating the vibrational states of three types of penta-atomic molecules, e.g., semi-rigid CH4, floppy H3O2−, and the van der Waals complex He3Cl2, for numerical demonstrations. Future Plans Kinetics and dynamics study of combustion-related reactions We will continue to study some important combustion reactions using the direct ab initio molecular dynamics program. Our study of a series of reactions involving the HOCO radical will conclude with the disproportionation of the HOCO radical. Here we will address the energies, geometries, and vibrational frequencies of the stationary points on the singlet ground-state surface, and the reaction mechanism. If one HOCO radical abstracts the hydrogen atom from the other, the products would be HC(O)OH and CO2. If the two HOCO radicals form an intermediate oxalic acid (HOC(O)C(O)OH) complex, the products could be H2O, CO and CO2, or two CO2 and H2. The dynamics will be carried out using a dual level ab initio method. The aim of this research is to determine the mechanism and product branching ratio as well as rate coefficients. A new direction in the study of combustion-related radical reactions using the direct ab initio molecular dynamics program will focus on the kinetics and dynamics of cyclic, N- and O-containing fuel molecules. The concentration of cyclic compounds in diesels and other future transportation fuels, produced largely from non-traditional sources such as oil shales and sand oils, are much higher than those in current fuels. There are only limited kinetics data on cyclic fuel molecules, yet they are required to design future internal combustion engines using such fuels. A new unique step in the chemistry is the ring-opening processes resulting in, for example cyclopentoxy (cyc-C5H9O) radicals discussed by us before. Such radicals may well contribute to enhanced formation of soot without a ring-opening reaction. In this work, we will start this project with the reactions of morpholine (1-oxa-4-aza-cyclohexane, i.e. cyclic −OCH2CH2NHCH2CH2−) and its derivatives with small radicals such as O2, HO2 and OH. Westmoreland et al. have recently demonstrated that morpholine is an ideal compound for modeling those hydrocarbon, oxygenated and N-containing fuels. Here, we will address the energies, geometries, and vibrational frequencies of the stationary points on the ground-state surfaces, and the reaction mechanism. The dynamics will be carried out using the DualOrthGT program, together with variational RRKM theory. Vibronic spectrum calculations of CH2 and its interactions with He In our GPMD group, Sears and Hall have observed rich and complicated rovibronic levels of CH2 near the C + H2 and CH + H dissociation limits. They provide a challenge for multiple surface dynamics theory, with relevance to the reactive system as well as CH2 spectroscopy. We have calculated five low-lying electronic potential energy surfaces of CH2 using a multireference CI (MRCI) method. The adiabatic surfaces will be transformed into a set of diabatic ones using the quasi-adiababatic approximation of Koppel et al. Full-dimensional quantum dynamics will then be performed on the five coupled surfaces. The principal interest is in the energy levels and non-adiadiabatic coupling effects, for detailed comparison with experimental observations. In addition, we also plan to calculate the singlet and triplet potential energy surfaces of the He-CH2 (X/A) interaction system using the CCSD(T)/aug-cc-pVQZ level of theory. The surfaces will be used for investigating the dynamics of singlet and triplet states of CH2 in collaboration with Tscherbul at Harvard, and rotationally inelastic scattering calculations in collaboration with Dagdigian and Alexander at Johns Hopkins and Maryland.  Non-adiabatic molecular dynamics studies of polyatomic molecular reactions Electronically excited species such as 1CH2 also play an important role in combustion chemistry. However, the studies of their reactivity are rather limited, partially due to the non-adiabatic dynamics effects because those reactions often occur on multiple potential energy surfaces. In this research, we will extend the surface hopping direct ab initio molecular dynamics algorithm, developed for the SECH MD studies, to simulate the bimolecular reactions and the photo-dissociation chemistry. The first application would be the photodissociation dynamics of acetone at 193-230 nm. This system has been investigated by Suits et al. using an universal ion imaging technique. The photon excited acetones produce two major types of products: CH3CO + CH3 and CO + 2CH3. The latter products result from poorly understood dissociation mechanisms. Here we will attempt to explore the dissociation pathways of acetone on its three low-lying electronic states. Publications since 2008 H.-G. Yu, G. Poggi, J.S. Francisco and J. T. Muckerman, Energetics and molecular dynamics of the reaction of HOCO with HO2 radicals, J. Chem. Phys. 129, 214307 (2008). H.-G. Yu, J.S. Francisco and J. T. Muckerman, Ab initio and direct dynamics study of the reaction of Cl atoms with HOCO, J. Chem. Phys. 129, 064301 (2008). H.-G. Yu and J.S. Francisco, Energetics and kinetics of the reaction of HOCO with hydrogen atoms, J. Chem. Phys. 128, 244315 (2008). H.-G. Yu, A spherical electron cloud hopping model for studying product branching ratios of dissociative recombination, J. Chem. Phys. 128, 194106 (2008). B.J. Braams and H.-G. Yu, Potential energy surface and quantum dynamics study of rovibrational states of HO3(X2A”), Phys. Chem. Chem. Phys. 10, 3150 (2008). W.-Q. Han, H.-G. Yu, C. Zhi, J. Wang, Z. Liu, T. Sekiguchi and Y. Bando, Isotope effect on band gap and radiative transitions properties of boron nitride nanotubes, Nano Lett. 10, 491 (2008). H.-G. Yu and J.S. Francisco, A theoretical study of the reaction of CH3 with HOCO radicals , J. Phys. Chem. A, 113, 3844 (2009). H.-G. Yu and J.S. Francisco, Ab initio and RRKM study of the reaction of ClO with HOCO radicals, J. Phys. Chem. A, 113, 12932 (2009). H.-G. Yu, Product branching ratios of the reaction of CO with H3+ and H2D+, Astrophys. J. Lett., 706, L52 (2009). H.-G. Yu, Spherical electron cloud hopping molecular dynamics simulation on dissociative recombination of protonated water, J. Phys. Chem. A, 113, 6555 (2009). H.-G. Yu, A general rigorous quantum dynamics algorithm to calculate vibrational energy levels of pentaatomic molecules, J. Mol. Spectrosc. 256, 287 (2009). 

Gas-Phase Molecular Dynamics: Theoretical Studies in Spectroscopy and Chemical Dynamics

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