A method is devised for treating the transfer of a light particle such as a hydrogen atom or a proton between two heavy particles, for the case of a collinear symmetric reaction AH+A→A+HA. Polar coordinates (ρ,ϑ) with origin at the origin of the usual mass‐weighted skewed‐angle potential energy contour plot are employed to simplify the calculation. Symmetric and antisymmetric vibrationally adiabatic states are obtained at each ρ. They provide an effective potential for the ρ motion and are used to obtain the elastic adiabatic phase shifts for the ρ motion and from them the transfer probability. The ρ motion corresponds approximately to that of the heavy particles and the ϑ to that of the light one. Semiclassical limiting expressions are obtained and provide a description of light particle tunneling at low energies for heavy–light–heavy particle systems. Numerical results are given and the present approximation is good for the systems investigated.

/pdf/dynamics-of-hydrogen-atom-and-proton-transfer-reactions-53kc6id6up.pdf

Dynamics of hydrogen atom and proton transfer reactions. Symmetric case

In a crossed molecular beam experiment, time‐of‐flight distributions of HD‐molecules scattered from Ne at an energy of 31.5 meV have been measured using the pseudorandom chopper method. Each time‐of‐flight spectrum shows a clearly resolved inelastic peak due to rotational excitation of HD from j=0 to j=1. With the aid of these spectra, together with additional measurements of the total differential cross section, the angular dependence of the differential cross section for the excitation j=0→1 is derived over a large angular range (20° to 120°). The sensitivity of the data to the interaction potential is carefully studied and the measured inelastic differential cross sections are compared with calculations based on interaction potentials recently proposed for this system.

Differential cross sections for the j=0→1 rotational excitation in HD–Ne collisions and their relevance to the anisotropic interaction

The nature of hydrogen bonding in the complexes NN–HF and OC–HF, as revealed from detailed ab initio electronic structure calculations, is unlike the bonding in the isoelectronic HCN–HF complex. The strong dipole–dipole attraction in HCN–HF is absent in the other two complexes. Competing effects that are possible in all hydrogen bonds are unmasked in NN–HF and OC–HF. Calculations have been performed with a number of large basis sets, extensive treatment of electron correlation, energetic partitioning, and evaluation of molecular properties. The potential energy surfaces that were generated demonstrate the linearity of the equilibrium structures, and show roughly comparable flexibility for bending, thus refining somewhat the experimentally inferred picture. In NN–HF and OC–HF, less than one‐half of the hydrogen bond strength of each is due to just the interaction of the unrelaxed charge distributions of the monomers; while polarization of monomer electron distributions accounts for most of the remaining attraction. There is consequently a substantial electric dipole moment enhancement. The total correlation effect is responsible for about one‐third of the well depth in NN–HF and OC–HF. Charge transfer is unimportant in all three complexes.

The nature of hydrogen bonding in the NN–HF, OC–HF, and HCN–HF complexes

A method for approximate treatment of collinear H atom or proton transfer reactions AH+B → A+HB which involve two nearly degenerate vibrational states is developed. The method is based on constructing a diabatic representation of the problem, i.e., one in which the reactant and the product vibrational states are distinguished as such throughout the collision. The diabatic representation is constructed with the aid of the adiabatic one discussed in an earlier paper. The treatment can also be applied to symmetric exchange reactions, in which case it yields good agreement with other results.

/pdf/dynamics-of-hydrogen-atom-and-proton-transfer-reactions-1l0v6e81xj.pdf

Dynamics of hydrogen atom and proton transfer reactions. Nearly degenerate asymmetric case

Density functional theory (DFT) has been used to calculate the vibrational Stark tuning rates of a variety of nitriles and carbonyls in quantitative agreement with experimental values with a correction factor of f=1.1 for the local electric field. These calculations show that the vibrational Stark tuning rate has an anharmonic contribution and a contribution due to geometric distortions caused in the molecules due to the applied electric field. The anharmonic and geometric distortion components of the vibrational Stark tuning rate were calculated by the frequency dependence of the CN or CO stretching mode with varying applied electric fields by using the optimized structure in zero applied field or allowing the structure to optimize in the applied electric field, respectively. The changes in the calculated frequency of the CN or CO stretching mode, bond length, and dipole moment of this bond with varying applied electric fields are shown. The transition polarizability and the difference polarizability were also calculated by DFT for comparison to the experimental data on nitriles and carbonyls. The DFT calculations suggest that the sign of the transition polarizability is negative and this result in turn has an effect on the experimental data analysis since the sign of the transition polarizability is not determined by experiment.

A quantitative theory and computational approach for the vibrational Stark effect

On quantal bound state solutions and potential energy surface fitting. A comparison of the finite element, Numerov-Cooley and finite difference methods

A study is made of the ’’conservation of the total cross section’’ and the ’’equivalence of the total cross section’’ rules for scattering from H2. It is shown that these rules are a better approximation than the random phase approximation would indicate. Cross section formulas are given for scattering atoms from mj state selected molecules and it is shown that total cross sections for state selected molecules depend on the anisotropic part of the interaction potential, while the spin‐averaged total cross section often depends only on the spherically symmetric part of the interaction potential. The total spin‐averaged cross section is thus independent of the initial rotation state of the molecule and depends only on the relative collision energy. It is further demonstrated that isotopic substitution, which shifts the center of mass changing the symmetric part of the interaction potential, has too small an effect on the total cross section to be useful as a means of determining the anisotropy of the potential.

On the use of total cross sections for obtaining the anisotropic interaction potential in atom–diatom system

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On quantal bound state solutions and potential energy surface fitting. A comparison of the finite element, Numerov-Cooley and finite difference methods

On the use of total cross sections for obtaining the anisotropic interaction potential in atom–diatom system