Excitation of degenerate vibrations in non-degenerate electronic bands

The vibrational rule structuic of the 2A'₁ band in the photoelectron spectrum of BF₃ is analyzed Using ab initio calculated coupling constants, It is shown that some lines of this spectrum represent excitation of single quanta of the degenerate stretching vibration They borrow their intensity from the adjacent 2E' state via a pseudo-Jahn-Teller interaction     

Interatomic decay of inner-valence-excited states in clusters

In an isolated atom, excitation of an inner valence electron above the outer valence subshell leads to creation of an autoionizing state. Recently, it has been demonstrated experimentally that in a cluster, the inner-valence-excited states can decay also by an interatomic mechanism which has been called resonant interatomic Coulombic decay (RICD). Here we show that RICD is indeed the leading but not the only possible interatomic decay mode of the inner-valence excitations in clusters. Using Ne (2s-->3p) excitation in MgNe cluster as an example, we explore the possible decay mechanisms and draw conclusions on their relative importance and on the nature of the corresponding decay products.     

Short-time dynamics through conical intersections in macrosystems. I. Theory: effective-mode formulation

The short-time dynamics through a conical intersection of a macrosystem comprising a large number of nuclear degrees of freedom (modes) is investigated. The macrosystem is decomposed into a "system" part carrying a limited number of modes, and an "environment" part. An orthogonal transformation in the environment's space is introduced, as a result of which a subset of three effective modes can be identified which couple directly to the electronic subsystem. Together with the system's modes, these govern the short-time dynamics of the overall macrosystem. The remaining environmental modes couple, in turn, to the effective modes and become relevant at longer times. In this paper, we present the derivation of the effective Hamiltonian, first introduced by Cederbaum et al. [Phys. Rev. Lett. 94, 113003 (2005)], and analyze its properties in some detail. Several special cases and topological aspects are discussed.     

Particle-number-dependent theory of few- and many-body systems

The introduction of approximations to evaluate physical properties of few- or many-body systems may violate exact symmetries and conservation laws. If, for example, the numberN of particles is incorrectly reproduced by the approximation, it can be shown that the optical potential for scattering of charged particles exhibits a spurious long-range potential. It is suggested to correct forN by introducing a particle-number-dependent interaction into the Hamiltonian, which does not influence exact results but changes the results of the approximation. The interaction is such that the original working equations of the approximation scheme undergo a trivial change only. As an example a simple model is investigated. It is found that restoringN also substantially improves all observables of the system.     

Impact of sulfur vs oxygen on the low-lying excited states of trans-p-coumaric acid and trans-p-coumaric thio acid

The low-lying excited singlet states of trans-p-coumaric acid (CA) and trans-p-coumaric thio acid (CTA) are investigated in view of characterizing the chromophore of the photoactive yellow protein (PYP), with particular regard to the impact of sulfur on the chromophore's electronic structure. The comparative ab initio study, performed with the highly accurate EOM-CCSD method, shows that the electronic state ordering upon vertical excitation and following in-plane geometry relaxation indeed depends in a very sensitive fashion on the presence of either sulfur or oxygen. The study identifies three relevant excited singlet states, two of which are of pi-pi type while the third state is of n-pi character. The study highlights the role of the latter n-pi state which is shown to be the lowest-lying excited state of CTA at all in-plane geometries under consideration, whereas this is not the case for CA.     

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.