Semirigid Vibrating Rotor Target Model Research Articles

Isotope effects of quantum dynamics for the Cl + CH 4/CD 4 reaction

Based on a recently developed potential energy surface and the semi-rigid vibrating rotor target model, a time-dependent wave packet dynamic study for the isotope effects of the Cl + CH 4/CD 4 reactions was conducted. The initial state-specific probabilities exhibited the replacement of hydrogen by deuterium significantly decreased the reaction ability, and the rovibrational excitations of the methane molecule favored the progress of the reaction. Additionally, the ground state rate constants are reported and compared with the experimental and other theoretical ones.

Quantum dynamics study of H+NH3→H2+NH2 reaction

We report in this paper a quantum dynamics study for the reaction H+NH3-->NH2+H2 on the potential energy surface of Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The quantum dynamics calculation employs the semirigid vibrating rotor target model [J. Z. H. Zhang, J. Chem. Phys. 111, 3929 (1999)] and time-dependent wave packet method to propagate the wave function. Initial state-specific reaction probabilities are obtained, and an energy correction scheme is employed to account for zero point energy changes for the neglected degrees of freedom in the dynamics treatment. Tunneling effect is observed in the energy dependency of reaction probability, similar to those found in H+CH4 reaction. The influence of rovibrational excitation on reaction probability and stereodynamical effect are investigated. Reaction rate constants from the initial ground state are calculated and are compared to those from the transition state theory and experimental measurement.

Comparison between different reactions of group IV hydride with H

The four-dimensional time-dependent quantum dynamics calculations for reactions of group IV hydride with H are carried out by employing the semirigid vibrating rotor target model and the time-dependent wave packet method. The reaction possibility, cross section and rate constants for reactions (H+SiH 4 and H+GeH 4 ) in different initial vibrational and rotational states are obtained. The common feature for such kind of reaction process is summarized. The theoretical result is consistent with available measurement, which indicates the credibility of this theory and the potential energy surface.

Time-dependent wave packet study for D + DCN reaction with SVRT model

Time-dependent wave packet calculation for the D + DCN reaction is carried out employing TSH3 potential energy surface [M.A. terHorst, G.C. schatz, L.B. Harting, J. Chem. Phys. 105 (1996) 558] with the semirigid vibrating rotor target (SVRT) model [J.Z.H. Zhang, J. Chem. Phys. 111 (1999) 3929]. We calculated the total reaction probabilities from the initial ground ro-vibrational state for various values of total angular momentum J. The reaction cross sections and rate constants are also calculated and compared with the previous results for the isotopic reaction H + HCN on the same potential energy surface.

Stereodynamics and Rovibrational Effect forH+NH3→H2+NH2 Reaction

We employ the semirigid vibrating rotor target (SVRT) model to studythe influence of rotational and vibrational excitation of the reagenton reactivity for the reaction H+NH3. The excitation of thepseudo H–NH2 stretching vibration of the SVRT model givessignificant enhancement of reaction probability. Detailed study of theinfluence of initial rotational states on reaction probability showsstrong steric effect. The steric effect of polyatomic reactions,treated by the SVRT model, is more complex and richer than theoreticalcalculations involving linear molecular models.

Quantum dynamics study of isotope effect for H+CH4 reaction using the SVRT model

The semirigid vibrating rotor target model is applied to study the isotope effect in reaction H+CH4→H2+CH3 using time-dependent wave-packet method. The reaction probabilities for producing H2 and HD product channels are calculated. The energy dependence of the reaction probabilities shows oscillating structures for both reaction channels. At low temperature or collision energies, the H atom abstraction is favored due to tunnelling effect. In partially deuterated CHxDy (x+y=4), the breaking of the C–H bond is favored over that of the C–D bond in the entire energy range studied. In H+CHD3 reaction at high energies, the HD product dominates simply due to statistical factor.

Semirigid vibrating rotor target model for CH4 dissociation on a Ni(111) surface

We present a theoretical treatment of the semirigid vibrating rotor target model to study dissociative chemisorption of CH4 at the atop site on Ni(111) surface. In this treatment, the fixed-site approximation is used to study chemisorption of methane on Ni treated as a rigid and locally flat surface. This results in a four-dimensional (4D) theoretical model to treat methane dissociation on Ni. Using parameters from ab initio calculations, an empirical potential energy surface is constructed for the CH4/Ni(111) system over the atop site. A 4D quantum dynamics calculation using the time-dependent wave-packet method is carried out on this potential energy surface. Our calculation shows that the dissociation probability of methane is an increasing function of kinetic energy, and the C–H stretching vibration significantly enhances the dissociation. The dissociation probability has a strong dependence on the initial orientation of the molecule. Reasonably good agreement is found between the current theoretical calculation and experimental results.

Time-dependent quantum wave packet study of the H+DCN→HD+CN reaction

Time-dependent wave packet calculation for the reaction H+DCN→HD+CN is carried out using the semirigid vibrating rotor target model [J. Z. H. Zhang, J. Chem. Phys. 111, 3929 (1999)] on the TSH3 potential energy surface [J. Chem. Phys. 105, 558 (1996)]. Reaction probabilities are calculated from various initial rovibrational states of the reagent. Reaction cross sections and rate constants are calculated and are compared with the previous results for the isotopic reaction H+HCN on the same potential energy surface.

Generalized semirigid vibrating rotor target model for atom–poly reaction: Inclusion of umbrella mode for H+CH4 reaction

In this work, we present a generalized version of the semirigid vibrating rotor target (SVRT) model by including additional vibrational modes explicitly in the SVRT Hamiltonian. The inclusion of additional vibrational modes eliminates the uncertainty of fixing certain geometries of the target molecule as required in the basic SVRT model. This generalized SVRT (GSVRT) model was employed to study the benchmark reaction H+CH4 by including the umbrella mode of CH4. Influence of the umbrella mode of the reagent on reactivity is investigated. It is concluded that the inclusion of the umbrella vibrational mode of CH4 has only a small effect on the reaction from the ground state of the reagent, and essentially no effect from the excited C–H stretching vibrational state of the reagent. However, the initial excitation of the umbrella mode does give a sizable enhancement of reaction and reduces the reaction barrier by about 1.1 kcal/mol.

Time-dependent quantum wave packet study of H+HCN→H2+CN reaction

Time-dependent quantum wavepacket calculations for the H+HCN reaction are carried out on the ab initio potential energy surface of ter Horst et al. [J. Chem. Phys. 105, 558 (1996)]. The dynamics calculations are performed using both the semirigid vibrating rotor target (SVRT) model [J. Chem. Phys. 111, 3929 (1999)] as well as the pseudo atom–diatom model. Total reaction probabilities from the initial ground state of the reagent are calculated for various values of the total angular momentum quantum number J. Reaction cross sections and rate constants are also calculated. The dynamical result from the SVRT calculation is compared with that from a pseudo atom–diatom calculation in which the HCN is treated as a pseudo diatom. Both the SVRT and pseudo atom–diatom calculations involve three degrees of freedom for the H+HCN reaction due to linearity of the HCN molecule at both reactant and transition states. The results from these two calculations are generally close to each other with some difference at high collision energies. The two models for the current system are essentially the same except that the rotational constant used is different. In particular, the SVRT model uses the correct rotational constant for the linear HCN molecule while the pseudo atom–diatom model produces a rotational constant which is much larger than the correct one.

SVRT calculation for bond-selective reaction H+HOD→H2+OD, HD+OH

The semirigid vibrating rotor target (SVRT) model is applied to study bond-selective branching reaction H+HOD→H2+OD, HD+OH on the Schatz–Elgersma potential energy surface when one of the stretching modes of HOD is excited. Using the SVRT model, the time-dependent wavepacket calculation is carried out in four-mathematical dimensions with the remaining two internal coordinates fixed. The reaction probabilities for producing two product branches are calculated from two separate dynamics calculations. The results show that for reaction H+HOD(100)→HD+OH when O–D stretching mode is excited, the SVRT calculation gives excellent results. The SVRT result is slightly worse for reaction H+HOD(001)→H2+OD when the O–H stretching mode is excited. The current study demonstrates that the SVRT model is also applicable for giving accurate results for polyatomic reactions when the chemical bond that is broken is vibrationally excited.

Stereodynamics and rovibrational effect for H+CH4(v,j,K,n)→H2+CH3 reaction

In this work, we employ the semirigid vibrating rotor target (SVRT) model to study the influence of rotational and vibrational excitation of the reagent on reactivity for the benchmark reaction H+CH4(v,j,K,n). The excitation of the pseudo H–CH3 stretching vibration of the SVRT model gives significant enhancement of reaction probability, consistent with the later position of the reaction barrier on the potential energy surface. The vibrationally thermal-averaged rate constant is much larger than the rate constant of the ground vibrational state. Detailed study of the influence of initial rotational states on reaction probability shows strong steric effect. The reaction probability is directly correlated with the angular distribution of the initial wave function determined by different angular momentum relationships among three vectors j, R, and r. The steric effect of polyatomic reactions, treated by the SVRT model, is more complex and richer than theoretical calculations involving linear molecular models.

Semirigid vibrating rotor target calculation for reaction H+HOD→H2+OD, HD+OH

The semirigid vibrating rotor target (SVRT) model is applied to study the branching reaction H+HOD→H2+OD, HD+OH on the Schatz–Elgersma potential energy surface. Using the SVRT model, the time-dependent wave packet calculation is carried out in four-mathematical dimensions with the two additional internal coordinates fixed at/near transition state geometries. The reaction probabilities for producing two product branches are calculated from two separate dynamics calculations. Comparison with results from the six-dimensional dynamics calculation shows that the SVRT reaction probabilities and cross sections for both branching products are accurate within a wide range of collision energy. This shows that the SVRT model is capable of giving quantitatively accurate dynamics information for polyatomic reactions.

Application of Semirigid Vibrating Rotor Target Model to the Reaction of O(3P) + CH4 → CH3 + OH

In this paper, the SVRT (semirigid vibrating rotor target) model has been applied to study the reaction of O(3P) + CH4 → CH3 + OH using the time-dependent wave packet (TDWP) method. Employing the basic SVRT model, quantum dynamics calculation for any atom−polyatom reaction involves only four mathematical dimensions (4D). The reaction probability, cross section, and rate constant from the initial ground state are calculated for the title reaction on potential energy surfaces of Corchado et al. (C-T) and Jordon and Gilbert (JG). The calculated reaction probabilities on the C-T surface are significantly smaller than those calculated on the JG surface. The difference in barrier height is insufficient to account for the difference in the magnitude of reaction probabilities on two surfaces. Instead, global contour plots show that the C-T surface appears to have incorrect contour lines near the reaction region which tend to help reflect the wave packet back toward the entrance channel. On the other hand, our cal...

Application of semirigid vibrating rotor target model to reaction of H+CH4→CH3+H2

The SVRT (semirigid vibrating rotor target) model is applied to study the reaction of H+CH4→CH3+H2 using time-dependent wave packet (TDWP) method. Applying the basic SVRT model, reliable quantum dynamics calculation for any atom–polyatom reaction can be carried out in four mathematical dimensions (4D) only. In the current study, reaction probability, cross-section, and rate constant are calculated for the title reaction from the ground state of the reagent. The energy dependence of the calculated reaction probability shows oscillatory structures, similar to those observed in the H+H2 reaction. Those structures are generally associated with broad dynamical resonances and are washed out in the energy dependence of integral cross-sections due to summation over partial waves. Our calculated rate constant is in good agreement with experimental measurement. The present results demonstrate that the SVRT model for atom–polyatomic reaction provides a practical and accurate approach for studying chemical reactions involving polyatomic molecules.

The semirigid vibrating rotor target model for atom-polyatom reaction: Application to H+H2O→H2+OH

The semirigid vibrating rotor target (SVRT) model for the polyatomic reaction has been applied to the reaction of H+H2O→H2+OH using the time-dependent wave packet approach. Since the SVRT model for a general atom–polyatom reaction involves only four-mathematical dimensions (4D), the SVRT dynamics calculation for H+H2O requires much less computational effort than the exact full-dimensional treatment. Numerical calculation shows that by properly choosing the values for the excluded degrees of freedom, excellent results are obtained for the computed reaction probability, cross section, and rate constant. The present numerical calculation for H+H2O reaction from the initial ground state clearly demonstrates that the SVRT model for the polyatomic reaction provides an accurate and practical approach for computational study of chemical reactions involving polyatomic molecules.

The semirigid vibrating rotor target model for quantum polyatomic reaction dynamics

In this paper, we present detailed quantum treatment of the semirigid vibrating rotor target (SVRT) model for reaction dynamics involving polyatomic molecules. In the SVRT model, the reacting (target) molecule is treated as a semirigid vibrating rotor which can be considered as a three-dimensional generalization of the diatomic molecule. This model provides a realistic framework to treat reaction dynamics of polyatomic systems. Using the SVRT model, it becomes computationally practical to carry out quantitatively accurate quantum dynamics calculation for a variety of dynamics problems in which the reacting molecule is a polyatomic or complex molecule. In this work, specific theoretical treatment and mathematical formulation of the SVRT model are presented for three general classes of reaction systems: (1) reaction of an atom with a polyatomic molecule (atom–polyatom reaction), (2) reaction between two polyatomic molecules (polyatom–polyatom reaction), and (3) polyatomic reaction with a rigid surface (polyatom–surface reaction). Since the number of dynamical degrees of freedom in the SVRT model for the above three classes of dynamical problems is limited, accurate quantum (both ab initio and dynamical) calculations are possible for many reactions of practical chemical interest. In this paper, a time-dependent wave packet approach is employed to implement the SVRT model for dynamics calculation of polyatomic reactions.