Michael Baer

Adiabatic and diabatic representations for atom-diatom collisions: Treatment of the three-dimensional case

A previous treatment of the adiabatic and diabatic representations for an atom-diatom system in the frame of the collinear arrangement is extended to three dimensions. It is found that the diabatic form of the Schrodinger equation, in contrast to the adiabatic form, is simple and very similar to that encountered in the single surface case. Therefore all tecniques, including the various approximations that have recently been introduced in order to solve the single surface case, can now be directly applied to the multiple surface equation.

Incorporation of electronically nonadiabatic effects into bimolecular reactive systems. II. The collinear (H2 + H+, H2+ + H) system

Abstract An exact quantum mechanical study of the collinear reactive (H 2 + H + , H 2 + + H) system with the emphasis on electronic nonadiabatic processes is presented. This system was studied both ignoring nonadiabatic effects (i.e. a single surface calculation) and incorporating them. It was found that two features, i.e. the fact that the three interacting particles have identical masses and the existence of a deep potential well in the interaction region (in the lower surface) make this system very different from any other, including its isotopic analogs. Electronic transition probabilities were calculated as a function of energy and initial vibrational state. It was established that the charge transfer process takes place due to favorable resonance conditions between high vibrational states in the lower surface and corresponding states in the upper surface. If the initia state is above the threshold for charge transfer, the process is direct (and therefore adiabatic as far as the total internal energy is concerned), and if it is below then the process takes place in the vicinity, of the interaction region where high vibrational states of the lower surface are populated due to the deep potential well in the interaction region. Applying the information theoretical approach a surprisal analysis of the results was performed. It was found that most of the results for both the one-and the two-surface cases fit the predicted behavior due to this approach very ni

Collinear quantum mechanical calculations of the He + H+2 proton transfer reactions☆

Abstract Exact quantum mechanical results for collinear He + H + 2 → H + HeH + reactive collisions are presented for the (total) energy range of 0.93 cV to 1.4 eV. The H + 2 initial vibrational states include ν = 0 through ν = 5. The diatomics-in-molecules semi-empirical surface of Kuntz is used in the computations. Except for a short range of energies, the calculated reaction probabilities of H + 2 (ν = 0) are larger than those of excited H + 2 .

The collinear Cl + XY system (X,Y=H,D,T). A comparison between quantum mechanical, classical, and transition state theory results

In this work, exact quantum mechanical (QM) and classical (CL) transition probabilities for the Cl+XY (X,Y=H,D,T) collinear system are compared. The calculations were performed using a semiempirical LEPS surface. The main features discussed are tunneling and threshold behavior for both the ground state and the first excited state of the hydrogen molecule. In the second part, kinetic isotope effects are presented and discussed. Those were calculated in three different ways, using (i) QM transition probabilities, (ii) CL transition probabilities, and (iii) transition state theory (TST‐1D). Tunneling coefficients kQM/kCL and kQM/kTST were calculated and discussed. Finally, a brief comparison with experimental data was performed.

Comparison of quantum mechanical and quasi-classical calculations of collinear reaction rate constants for the H+Cl2 and D+Cl2 systems

Comparison between quantum and classical mechanical reaction probabilities and rate constants for the collinear H + Cl2 and D + Cl2 systems is made. Different quasi-classical methods are compared and the QCRF method which fulfils the principle of detailed balance is suggested. Finally the total reaction rate constants are compared with results obtained from a simple transition state model.

Infinite order sudden approximation for reactive scattering within classical mechanics. I. Theory

An infinite order sudden approximation for treating reactive scattering within classical mechanics is presented. It is shown that requiring the conservation of total energy in the subspace formed by applying this approximation is enough to define, for any given set of initial conditions, a unique trajectory which moves from the reagents to the products arrangement channel. A detailed description of how to apply this method for any three‐atom reactive system is given.

Electronic nonadiabatic transitions in the reactive (Ar+ + H2, Ar + H+2, ArH+ + H) system. Numerical results for the collinear configuration

Abstract In this communication are presented exact quantum mechanical nonadiabatic electronic transition probabilities for the collinear reaction Ar+ + H2(vi = 0) → ArH+(vf) + H. The calculations were performed using a potential surface calculated by the DIM method. It is established that large probabilities (≈ 1.0) can be obtained only if there is enough translational energy to overcome a potential barrier formed due to the crossing between vi = 0 of the Ar+ + H2 system and vi = 2 of the Ar + H+2 system. The threshold for the reaction is found to be 0.06 eV.

Integral total reactive cross section calculations within the infinite order sudden approximation

Abstract The initiafl l -labelled reactive infinite order sudden (IOS) approximation as formulated recently by Khare et al. is used to calculate integral total cross sections for the H + H 2 reaction. Results are given over the energy range 0.5 to 1.0 eV. Comparisons with accurate converged close coupling (CC) and classical results are made and good agreement is obtained. The method should be useful in the theoretical analysis of experiments.

Integral cross sections for the reaction F + H2, (vi = 0) → HF(vf = 0,1,2,3) + H: a quantum-mechanical calculation within the infinite order sudden approximation

Abstract Integral reactive quantum-mechanical cross sections and product vibrational distributions are presented for the F + H 2 system. The calculations were made within the infinite order sudden approximation (IOSA) formalism and the results are compared with experimental data and results obtained with other treatments.

Coplanar and collinear quantum mechanical reactive scattering: The importance of virtual vibrational channels in the H+H2 exchange reaction

We have performed accurate quantum mechanical calculations nfor the coplanar H + H_2 exchange reaction, using sufficient rotational and vibrational basis functions in the close-coupling expansion to ensure convergence. We repeated these calculations with a converged rotational basis set but with only one vibrational basis function, in analogy to what Saxon and Light and Wolken and Karplus, respectively, did for the similar coplanar and three dimensional reaction. The vibrationally converged and one-vibration results differ substantially for the coplanar as well as the collinear reaction, indicating the crucial role played by virtual vibrational channels.