Potential-energy surfaces, unimolecular processes and spectroscopy

The present symposium brings together research in a number of fields: the quantum-chemical calculation of molecular potential-energy surfaces, rotational–vibrational spectroscopy, methods of calculating rotational–vibrational energy levels, unimolecular reactions and intramolecular dynamics. Several aspects of the work are discussed including some recent developments on rates and products' quantum state distributions for unimolecular dissociations having highly flexible transition states. The usefulness of having improved potential-energy surfaces, particularly the bonding and hindered rotational potentials in the dissociations, is noted. In various other studies in this symposium a better knowledge of the surfaces would be particularly helpful. New results on a semiclassical quantization method are also described

On the Theory of Intramolecular Energy Transfer

We consider the distinguishing features of two main types of classical anharmonic motion in molecules, their quantum parallels, and conditions that classical chaos also be sufficient for “quantum chaos”. Implications are considered for experimental reaction rates, R.R.K.M. theory, spectra and a possible type of system for intramolecular laser-selective chemistry. A theory of intramolecular energy transfer between two ligands of a heavy atom is described for a system which may contain many coordinates. It is partly statistical and, for the modes of each ligand which communicate through the heavy atom, dynamical

The second R. A. Robinson Memorial Lecture. Electron, proton and related transfers

Past and current developments in electron and proton transfer and in related fields are described. Broad classes of reactions have been considered from a unified viewpoint which offers a variety of experimental predictions. This introductory lecture considers various aspects of this many-faceted field. A simple equation is given for a highly exothermic electron-transfer reaction

Beyond the Historical Perspective on Hydrogen and Electron Transfers

A brief overview of proton and electron transfer history is given, and various features influencing enzymatic catalysis are discussed. Examples of generic behavior are considered, together with questions that can be addressed for both experimental and computational results. Examples of high and low pre-exponential factors A of the intrinsic rate constant k_H ranging from ~10^(17) s^(-1) to ~10^4 s^(-1) and normal (~10^(13)) are noted with significant error bars and discussed

Recent Developments in Electron Transfer Reactions

Earlier results and more recent developments in electron transfer reactions are reviewed. The more recent results include inverted behavior, electronic orientation effects on reaction rates, solvent dynamics, early steps in photosynthesis, and light emission from metal electrodes

Electron transfer theory and its inception

It is a pleasure to introduce this issue on electron transfer processes. The field has developed greatly and in many different directions not envisioned in the late 1940s. The modern electron transfer era began at that time in the form of studies on the simplest class of reactions in all of chemistry, isotopic exchange reactions of the electron transfer type. In their simplest form no chemical bonds are broken or formed, only an electron is transferred from one reactant to the other. I remember how surprised and excited I was reading in 1955 a paper by Bill Libby (W. F. Libby, J. Phys. Chem., 1952, 56, 893), written several years earlier, explaining why some of these reactions were slow and others fast. In his explanation he used the Franck–Condon principle to interpret the results: he noted that when an electron "jumped" from one reactant to the other the slow moving nuclei changed neither their positions nor their momenta during the jump, and what the consequences were. I was especially excited, since that principle had originally been introduced to explain molecular spectra rather than chemical reaction rates. But perhaps at this point I should say a few words on how I came into theoretical chemistry as a practitioner just a few years earlier

Sum frequency generation, calculation of absolute intensities, comparison with experiments, and two-field relaxation-based derivation

The experimental sum frequency generation (SFG) spectrum is the response to an infrared pulse and a visible pulse and is a highly surface-sensitive technique. We treat the surface dangling OH bonds at the air/water interface and focus on the absolute SFG intensities for the resonant terms, a focus that permits insight into the consequences of some approximations. For the polarization combinations, the calculated linewidths for the water interface dangling OH SFG band at 3,700 cm⁻¹ are, as usual, too large, because of the customary neglect of motional narrowing. The integrated spectrum is used to circumvent this problem and justified here using a Kubo-like formalism and theoretical integrated band intensities rather than peak intensities. Only relative SFG intensities are usually reported. The absolute integrated SFG intensities for three polarization combinations for sum frequency, visible, and infrared beams are computed. We use molecular dynamics and the dipole and the polarizability matrix elements obtained from infrared and Raman studies of H₂O vapor. The theoretical expressions for two of the absolute susceptibilities contain only a single term and agree with experiment to about a factor of 1.3, with no adjustable parameters. The Fresnel factors are included in that comparison. One of the susceptibilities contains instead four positive and negative terms and agrees less well. The expression for the SFG correlation function is normally derived from a statistical mechanical formulation using a time-evolving density matrix. We show how a derivation based on a two-field relaxation leads to the same final result

Emergency Responder’s Guide to Protecting the Edwards Aquifer: Instructional Enhancements

Coming soo

Theory of single-molecule controlled rotation experiments, predictions, tests, and comparison with stalling experiments in F_1-ATPase

A recently proposed chemomechanical group transfer theory of rotary biomolecular motors is applied to treat single-molecule controlled rotation experiments. In these experiments, single-molecule fluorescence is used to measure the binding and release rate constants of nucleotides by monitoring the occupancy of binding sites. It is shown how missed events of nucleotide binding and release in these experiments can be corrected using theory, with F1-ATP synthase as an example. The missed events are significant when the reverse rate is very fast. Using the theory the actual rate constants in the controlled rotation experiments and the corrections are predicted from independent data, including other single-molecule rotation and ensemble biochemical experiments. The effective torsional elastic constant is found to depend on the binding/releasing nucleotide, and it is smaller for ADP than for ATP. There is a good agreement, with no adjustable parameters, between the theoretical and experimental results of controlled rotation experiments and stalling experiments, for the range of angles where the data overlap. This agreement is perhaps all the more surprising because it occurs even though the binding and release of fluorescent nucleotides is monitored at single-site occupancy concentrations, whereas the stalling and free rotation experiments have multiple-site occupancy