A three-dimensional time-dependent quantum mechanical wavepacket method is used to calculate the state-to-state reaction probabilities at zero total angular momentum for the Li + HF → LiF +H reaction. Reaction probabilities starting from several different initial HF vibrational–rotational states (v=0,j=0,1,2) and going to all possible open channels are computed over a wide range of energies. A single computation of the wavepacket dynamics yields reaction probabilities from a specific initial quantum state of the reactants to all possible final states over a wide range of energies. The energy dependence of the reaction probabilities shows a broad background structure on which resonances of varying widths are superimposed. Sharp resonance features seem to dominate particularly at low product translational energies. There are marked changes in the energy dependence of the reaction probabilities for different initial or final diatom rotational quantum numbers, but it is noticeable that, for both reactants and products, odd and even rotational quantum numbers give rise to similar features. Our results clearly identify some resonance features which are present in the reaction probability plots for all product and initial states, though they appear in the form of sharp peaks in some plots and sharp dips in others. We speculate that these features arise from reactive scattering resonances which serve to redistribute the flux preferentially to particular product quantum states. The present calculations extend to higher energies than previously published time-independent reactive scattering calculations for this system.

Time-dependent quantum mechanical calculations have been carried out to estimate the total reactive cross sections, product branching ratios, and product quantum state distributions for the O( 1 D) + HCl reaction using both reactant and product Jacobi coordinates. The potential energy surface of T. Martinez et al. (Phys. Chem. Chem. Phys. 2000, 2, 589) has been used in the calculations. The theoretical predictions are compared with experimental results and with the results of classical trajectory calculations on the same surface. The comparisons demonstrate the suitability of the potential energy surface and provide useful insights into the reaction mechanism. The calculations using product Jacobi coordinates are the first calculations for this system which permit the prediction of state-to-state reaction probabilities and of product quantum state distributions.

Reactive scattering probabilities are computed over a wide range of collision energies for a model system based on the Li+HF→LiF+H reaction using both grid based time-dependent and time-independent quantum mechanical methods. The computations are carried out using a fixed Li–F–H angle which is chosen to be that at which the barrier to the chemical reaction is lowest. The calculated reaction probabilities for this system display many sharp features as a function of energy which are ascribed to scattering resonances. The time-independent calculations have been carried out on a very dense energy grid, thus permitting detailed comparison between time-independent and time-dependent methods (in the latter case, a single computation of the wave packet dynamics provides information on the energy dependence over a given energy range). The results show that the time-dependent calculations are capable of reproducing even the sharpest resonance features computed using the time-independent method. The time-dependent techniques are conceptually very simple and therefore easily implemented. The results presented also demonstrate that the grid based time-dependent quantum mechanical methods used here are able to describe threshold energy dependence of reaction probabilities where the exit channel kinetic energy is effectively zero. The nature of some of the resonance structures are investigated by computing the time-independent continuum wave functions at the ‘‘resonance’’ energies thus mapping out the nodal structure of the wave functions. The good agreement between time-independent and time-dependent methods is shown to be maintained when a centrifugal barrier is added to the potential to simulate the effect of nonzero orbital angular momentum.

ABSTRACT:The time-dependent real wave packet method has been used to study the C( 1 D) ϩ HD reaction. The state-to-state and state-to-all reactive scattering probabilities for a broad range of energies are calculated at zero total angular momentum. The probabilities for J Ͼ 0 are estimated from accurately computed J ϭ 0 probabilities by using the J-shifting approximation. The integral cross sections for a large energy range, and thermal rate constants are calculated.

Quantum mechanical wave packet calculations are carried out for the H((2)S) + FO((2)II) --> OH((2)II) + F((2)P) reaction on the adiabatic potential energy surface of the ground (3)A'' triplet state. The state-to-state and state-to-all reaction probabilities for total angular momentum J = 0 have been calculated. The probabilities for J > 0 have been estimated from the J = 0 results by using J-shifting approximation based on a capture model. Then, the integral cross sections and initial state-selected rate constants have been calculated. The calculations show that the initial state-selected reaction probabilities are dominated by many sharp peaks. The reaction cross section does not manifest any sharp oscillations and the initial state-selected rate constants are sensitive to the temperature.