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A study on calculations employing density functional theory indicate undergoing fragmentation, dicationic clusters of benzene, hexafluorobenzene, and naphthalene produced by sequential one-electron or sudden double-ionization experiments on the neutrals could relax through the formation of inter-ring covalent C-C bonds. The consequences of double ionization processes in molecular aromatic clusters are described.

A study on buckminsterfullerene clusters was conducted to analyze their temperature-dependent, Boltzmann-averaged, intermolecular dynamics. A simple hypothesis is presented to illustrate that most of these vibrations must possess harmonic spacing although the associated potentials must be anharmonic. Calculations of the rate constants for the intercage motions are shown to converge toward the solid-state value. Experimental methods and results are presented.

The rates of macrocyclic ring rotation in benzylic amide [2]catenanes in solvent models were analyzed using variable-temperature nuclear magnetic resonance imaging spectroscopy and molecular mechanics calculations. Findings suggested that solvent effects and structural modifications can result to variations in the interlocked macrocycle dynamics. Other factors dictating the rate of circumrotation of benzylic amide catenanes include steric effects from the passing of bulky groups, complex hydrogen bonding, multiple inter-macrocycle pi-pi stacking and the T-herringbone interactions.

The influence of thermally induced nuclear dynamics (molecular vibrations) in the initial electronic ground state on the valence orbital momentum profiles of furan has been theoretically investigated using two different approaches. The first of these approaches employs the principles of Born-Oppenheimer molecular dynamics, whereas the so-called harmonic analytical quantum mechanical approach resorts to an analytical decomposition of contributions arising from quantized harmonic vibrational eigenstates. In spite of their intrinsic differences, the two approaches enable consistent insights into the electron momentum distributions inferred from new measurements employing electron momentum spectroscopy and an electron impact energy of 1.2 keV. Both approaches point out in particular an appreciable influence of a few specific molecular vibrations of A1 symmetry on the 9a1 momentum profile, which can be unravelled from considerations on the symmetry characteristics of orbitals and their energy spacing. [ABSTRACT FROM AUTHOR]

Ionization of bromomethanes (CH3Br, CH2Br2, and CHBr3) upon collision with metastable He*(2 3S) atoms has been studied by means of collision-energy-resolved Penning ionization electron spectroscopy. Lone-pair (nBr) orbitals of Br4p characters have larger ionization cross sections than σC-Br orbitals. The collision-energy dependence of the partial ionization cross sections shows that the interaction potential between the molecule and the He*(2 3S) atom is highly anisotropic around CH3Br or CH2Br2, while isotropic attractive interactions are found for CHBr3. Bands observed at electron energies of ∼2 eV in the He*(2 3S) Penning ionization electron spectra (PIES) of CH2Br2 and CHBr3 have no counterpart in ultraviolet (He I) photoionization spectra and theoretical (third-order algebraic diagrammatic construction) one-electron and shake-up ionization spectra. Energy analysis of the processes involved demonstrates that these bands and further bands overlapping with σC-Br or πCH2 levels are related to autoionization of dissociating (He+-Br-) pairs. Similarly, a band at an electron energy of ∼1 eV in the He*(2 3S) PIES spectra of CH3Br has been ascribed to autoionizing Br** atoms released by dissociation of (unidentified) excited states of the target molecule. A further autoionization (S) band can be discerned at ∼1 eV below the lone-pair nBr bands in the He*(2 3S) PIES spectrum of CHBr3. This band has been ascribed to the decay of autoionizing Rydberg states of the target molecule (M**) into vibrationally excited states of the molecular ion. It was found that for this transition, the interaction potential that prevails in the entrance channel is merely attractive. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An exhaustive investigation of the outer-valence ionization spectra of azulene, phenanthrene, pyrene, chrysene, triphenylene, and perylene is presented. The analysis is based on one-particle Green’s function calculations performed upon correlated [density-functional theory/Becke three-parameter Lee–Yang–Parr (DFT/B3LYP)] geometries using the third-order outer-valence Green’s function [OVGF] and algebraic-diagrammatic construction [ADC(3)] schemes, as well as basis sets of improving quality (6-31G, 6-31G[sup *], cc-pVDZ). The ionization bands of polycyclic aromatic hydrocarbons show a great diversity, which reflects the strong impact of the molecular architecture on orbital energies. Despite the intricacy of ionization spectra and the extent of the shake-up contamination in the π- and σ-band systems, the ADC(3) results enable consistent insights into available ultraviolet photoelectron measurements, up to the inner-valence region. They also indirectly support recent assignments of low-lying π[sup *]←π doublet excitations in the electronic absorption spectrum of the pyrene and perylene cations by means of time-dependent density functional theory [J. Chem. Phys. 111, 8904 (1999)]. It has been found that OVGF pole strengths smaller than 0.85 very systematically foretell a breakdown of the orbital picture of ionization at the ADC(3) level. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A detailed study on the valence region, of the electronic structure, ionization spectrum, and electron momentum distributions of ethanol is presented. The results from the analysis reveal a strong influence of the molecular conformation on the outermost electron momentum distributions and quantitatively significant discrepancies attributed to strong dynamical disorder in the gas phase molecular structure.

The interplay between the valence electronic structure, the topology and reactivity of orbitals, and the molecular structure of biphenyl by means of Penning ionization electron spectroscopy in the gas phase upon collision with metastable He*(2(super 3)S) atoms, are studied. Results demonstrate that biphenyl molecule lying at the surface of polycrystalline layers adopt predominantly a planar configuration, and in an amorphous sample most molecules have twisted structures.

Comprehensive theoretical study of the He(I) UV photoionization spectra of coronene, 1.2, 6.7-dibenzopyrene, 1.12-benzoperylene, and anthanthrene is discussed. The OVGF/6-31G and OVGF/cc-pVDZ data demonstrate that the sensitivity of the one-electron binding energies to the basis set decreases with increasing binding energies.

The x-ray photoionization spectra of large saturated hydrocarbons have been investigated by means of one-particle Green’s function calculations. These spectra saturate overall rather quickly to their asymptotic form with increasing system size. The results obtained indicate a severe breakdown of the molecular orbital picture of ionization above a binding energy threshold of about 23 eV, for n-alkane chains ranging from n-propane to n-nonane, or cycloalkane compounds such as cyclobutane, cyclopentane, and cyclohexane. In spite of the fast multiplication of satellite solutions, shake-up lines remain confined above that threshold, as a result of the delocalization properties of one-electron canonical states. The ring closure is shown to emphasize the dispersion of photoionization intensity into satellites. Conformational changes, on the other hand, have only marginal effects on the convoluted correlation bands. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Density functional theory, along with the ωB97XD and UM06-2x exchange-correlation functional, has been used to study the reaction mechanisms and kinetics of the atmospheric oxidation of the main (kinetically dominant) thiophene-OH adduct [C4H4S-OH]• (R1) by molecular oxygen in its triplet electronic ground state. Kinetic rate constants and branching ratios under atmospheric pressure and in the fall-off regime have been calculated by means of transition state theory (TST), variational transition state theory (VTST) and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. In line with the computed energy profiles, the dominant process under both the thermodynamic and kinetic control of the reaction is O2 addition at the C5 position in syn mode. The computed branching ratios indicate that the regioselectivity of the reaction decreases with increasing temperature and decreasing pressure. [ABSTRACT FROM AUTHOR]