A study of the photoionisation dynamics of the cyanogen halides

Main group cyanides: from hydrogen cyanide to cyanido-complexes

Homoleptic cyanide compounds exist of almost all main group elements. While the alkali metals and alkaline earth metals form cyanide salts, the cyanides of the lighter main group elements occur mainly as covalent compounds. This review gives an overview of the status quo of main group element cyanides and cyanido complexes. Information about syntheses are included as well as applications, special substance properties, bond lengths, spectroscopic characteristics and computations. Cyanide chemistry is presented mainly from the field of inorganic chemistry, but aspects of chemical biology and astrophysics are also discussed in relation to cyano compounds.

Correlation effects in the photoelectron spectrum and photoionization dynamics of OsO4

The valence shell photoelectron spectrum of OsO₄⁺ is studied using the Dyson orbital theory and the photoionization cross-section and asymmetry parameters are analyzed by partial wave decomposition of the photoelectron.

The Role of Spin-Orbit Coupling in the Double-Ionization Photoelectron Spectra of XCN(2+) (X = Cl, Br, and I)

The photoelectron spectra of XCN(2+) (X = Cl, Br, and I) were calculated employing ab initio electronic structure methods with high-level electron correlation and explicit treatment of spin-orbit coupling. Twelve scalar-relativistic excited states of the dicationic systems, calculated from state-averaged CASSCF/MRCI calculations, were used as the electronic basis to evaluate spin-orbit eigenstates. While the spin-orbit effects in ClCN(2+) are found to be negligible, the electronic spectroscopy of BrCN(2+) and ICN(2+) is significantly influenced by interstate spin-orbit coupling. Several electronic degeneracies are lifted, and many unexpected accidental degeneracies occurred due to the spin-orbit coupling. In particular, the spin-orbit interactions between X̃ (3)Σ(-)-b̃ (1)Σ(+), Ã (3)Π-c̃ (1)Π, B̃ (3)Δ-ã (1)Δ, and C̃ (3)Σ(+)-d̃ (1)Σ(-) are found to be strong in BrCN(2+) and ICN(2+). By careful analysis of the effect of spin-orbit coupling parameters and the spin-orbit eigenstate composition, an assignment of the hitherto unidentified experimental photoelectron bands of BrCN(2+) and ICN(2+) is presented.

Molecular ionization energies and ground- and ionic-state properties using a non-Dyson electron propagator approach

An earlier proposed propagator method for the treatment of molecular ionization is tested in first applications. The method referred to as the non-Dyson third-order algebraic-diagrammatic construction [nD-ADC(3)] approximation for the electron propagator represents a computationally promising alternative to the existing Dyson ADC(3) method. The advantage of the nD-ADC(3) scheme is that the (N+/-1)-electronic parts of the one-particle Green's function are decoupled from each other and the corresponding equations can be solved separately. For a test of the method the nD-ADC(3) results for the vertical ionization transitions in C(2)H(4), CO, CS, F(2), H(2)CO, H(2)O, HF, N(2), and Ne are compared with available experimental and theoretical data including results of full configuration interaction (FCI) and coupled cluster computations. The mean error of the nD-ADC(3) ionization energies relative to the experimental and FCI results is about 0.2 eV. The nD-ADC(3) method, scaling as n(5) with the number of orbitals, requires the solution of a relatively simple Hermitian eigenvalue problem. The method renders access to ground-state properties such as dipole moments. Moreover, also one-electron properties of (N+/-1) electron states can now be studied as a consequence of a specific intermediate-state representation (ISR) formulation of the nD-ADC approach. Corresponding second-order ISR equations are presented.

The one-particle Green’s function method in the Dirac–Hartree–Fock framework. II. Third-order valence ionization energies of the noble gases, CO and ICN

In this paper we present the third-order extension of the four-component one-particle propagator method in the non-Dyson version of the algebraic diagrammatic construction (ADC) for the calculation of valence ionization energies. Relativistic and electron correlation effects are incorporated consistently by starting from the Dirac-Hamiltonian. The ADC equations derived from the Feynman diagrams can hereby be used in their spin-orbital form and need not be transformed to the spin-free version as required for a nonrelativistic treatment. For the calculation of the constant self-energy contribution the Dyson expansion method was implemented being superior to a perturbational treatment of sigma(infinity). The Dirac-Hartree-Fock- (DHF-) ADC(3) was applied to the calculation of valence photoionization spectra of the noble gas atoms, carbon monoxide and ICN now also reproducing spin-orbit features in the spectrum. Comparison with DHF-ADC(2), nonrelativistic ADC(3), and experimental data was made in order to demonstrate the characteristics and performance of the method.