On the statistical behaviour of molecular vibronic energy levels

Electronic spectra of polyatomic molecules often exhibit a high density of complicated energy levels, making a detailed analysis of the individual levels unfavourable. In these cases, statistical tests provide an appropriate means for analysing the spectra. Fluctuation measures are presented and evaluated for calculated and experimental molecular spectra as examples. The results are compared with the predictions of random matrix theory.     

Two-hole-one-particle configuration interaction approach for the ionization of open-shell molecules: Application to NO2

A special configuration interaction approach for the ionic states of open-shell molecules with a spatially nondegenerate ground state is presented. This approach takes into account all genuine one-hole and two-hole-one-particle excitations with respect to the ground state and allows for the determination of ionic energies and relative intensities for the whole energy range. A numerical application for NO₂ is reported providing in particular theoretical access to the inner-valence region where the interpretation of experimental data hitherto has been open to question.     

Green's function calculations on the complete valence ionization spectra of HF,HCl, HBr AND HI

The ionization spectra of the entire valence region are calculated for HF, HCl, HBr and HI. For the two ionization processes of lowest energy the common molecular orbital picture of ionization applies, whereas this picture breaks down for ionization from the inner valence α-orbital. For HF and HCl basis set effects on the calculated outer-valence ionization energies are investigated and accurate values are computed using large basis sets. The calculated inner valence ionization spectra are compared with recent (e, 2e)-measurements.     

What happens when several closely lying electronic states interact through nuclear motion?

The interaction of several closely lying electronic states through vibrational is discussed. It is shown that this interaction may give rise to strong non-adiabatic effects which are essential for understanding experimental findings. The inner-shell photoionization in N₂ is investigated as a specific case.     

Strong correlation effects in the ionisation of CS2

The Hell photoelectron spectrum of CS₂ is presented. This spectrum is investigated by two different Green's function calculations. For the outer valence region the origin and assignment of satellite lines of significant intensity is clarified. Strong final state correlation effects are found for the inner valence region showing the so-called breakdown of single-particle picture of ionisation.     

Intermolecular Coulombic decay in small biochemically relevant hydrogen-bonded systems

Intermolecular Coulombic decay (ICD) is a very fast and efficient relaxation pathway of ionized and excited molecules in environment. The ICD and related phenomena initiated by inner-valence ionization are explored for H(2)O···HCHO, H(2)O···H(2)CNH, H(2)O···NH(3), NH(3)···H(2)O, H(2)O···H(2)S, H(2)S···H(2)O, and H(2)O···H(2)O (p-donor···p-acceptor). This set of small hydrogen-bonded systems contains seven types of hydrogen bonding, which are typical for biochemistry, and thus its investigation provides insight into the processes that can take place in living tissues. In particular, an estimate of the ICD in biosystems interacting with water (their usual medium) is made. This decay mode is expected to be a source of low-energy electrons proven to be of extreme genotoxic nature. For the purpose of our study, we have used high-precision ab initio methods in optimizing the geometries and computing the single- and double-ionization spectra of formaldehyde-, formaldimine-, ammonia-, hydrogen sulfide-, and water-water complexes. The energy range of the emitted ICD electrons, as well as the kinetic energy of the dissociating ions produced by ICD, is also reported.     

Barrierless Single‐Electron‐Induced cis–trans Isomerization

Lowering the activation energy of a chemical reaction is an essential part in controlling chemical reactions. By attaching a single electron, a barrierless path for the cis–trans isomerization of maleonitrile on the anionic surface is formed. The anionic activation can be applied in both reaction directions, yielding the desired isomer. We identify the microscopic mechanism that leads to the formation of the barrierless route for the electron‐induced isomerization. The generalization to other chemical reactions is discussed.     

Peierls instabilities in one-dimensional systems with Jahn-Teller-active monomers

A one-dimensional system is investigated which consists of monomers with Jahn-Teller-active vibrational coordinates. Peierls distortions in the ground states of the half- and quarter-filled systems are studied as a function of the electron-lattice and Jahn-Teller coupling constants. For both degrees of filling and for all the values of the coupling constants the band structure of the ground state is doubly degenerate. The interrelation is discussed between the present system and systems where the active internal degrees of freedom are not of the Jahn-Teller type.