The energies and wavefunctions of the lowest singlet and triplet Rybderg states in H2O were calculated in the expansion basis self‐consistent‐field procedure for a single configuration A portion of the energy surface of the 1A′ Rydberg state for an HOH angle of 105° was determined that shows the asymmetric dissociation of this state into ground‐state H(2S) and OH(2Π) fragments The energy along the reaction coordinate is almost separable into a repulsion depending only on the center‐of‐mass separation and an attractive potential that depends only on the OH internuclear separation For the C2υ conformation a large basis set was used to approach the Hartree–Fock limit Using these functions a minimum was calculated in the generalized oscillator strength for the 1A1 → 1B1 transition as a function of the momentum transfer function or the electron scattering angle This behavior was then confirmed experimentally for an energy loss of 74 eV with an incident electron energy of 500 eV Such a minimum is a gener

Energy Surface and Generalized Oscillator Strength of the 1A″ Rydberg State of H2O

Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule.

Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction

Elastic, inelastic, and total energy unresolved differential cross sections for high energy electron scattering by the hydrogen molecule have been computed in the first Born approximation. An accurate wave function in the form of a 36‐term expansion in correlated Gaussian functions was used for the electronic ground state of H2. The computed quantities have been averaged over the zero point vibrations and over thermal populations of the rotational states. The results are compared with the data derived from experiments.

Energy unresolved differential cross section for electron scattering by H2

High-energy (25--28-keV) electron-impact spectroscopy (HEEIS) has been used to measure a relatively complete Bethe surface for molecular nitrogen. This surface, placed on an absolute scale by Bethe-sum-rule normalization of the generalized oscillator strength (GOS), has been employed to obtain the x-ray incoherent scattering factor {ital S}({ital K}) as a function of the momentum transfer {ital K} by use of a sum rule of the GOS. Ground-state correlation effects on {ital S}({ital K}) were obtained by comparing the experimental results with theory based on a near-Hartree-Fock molecular wave function. The results are compared with recent theoretical calculations of valence-shell correlation effects. It is argued that x-ray and electron-scattering experiments offer the most sensitive tests currently available for valence-shell electron-correlation effects in the ground electronic states of molecules. The results obtained coupled with available theory suggest that correlation effects on the one-electron density play a dominant role in the determination of the total correlation energy of the nitrogen molecule.

Experimental determination of ground-state correlation effects in molecular nitrogen.

The Born approximation is used to obtain differential and total cross sections for inelastic electron scattering from benzene. The three lowest excited singlet states are treated (i.e. those of symmetry 1B1u, 1B2u and 1E1u). Simple π-electron antisymmetric molecular orbitals are used as the electronic wave functions, and the cross sections are averaged and summed over rotational and vibrational states. The effects of vibronic interactions on the cross sections are included.

Electron impact spectroscopy III. Calculated cross sections for inelastic scattering from benzene

The quantum theory of electron scattering from molecules in the gas phase was developed Expressions that include the effects of chemical binding are presented and the intensity averages to be expected for various types of experiments are discussed in terms of the theory The quantum mechanical average over the rotational states of the molecule is shown to be reducible to the classical method of averaging rotational motion except in the case of extremely high energy resolution of the scattered electrons (auth)

T. Ando

Papers

The theory of electron scattering from molecules. i. theoretical development