Jiri Müller

Configuration interaction calculations of satellite structure in photoelectron spectra of H2O

Abstract Configuration interaction wavefunctions were computed for the satellite peaks in the core and the valence photoelectron spectra of H 2 O. Relative intensities were computed in the sudden approximation including electron correlation in the neutral ground state. The intensity profile of the O 1s ESCA spectrum is understood in terms of single excitations from the 3a 1 and the 1b 1 orbitals to low lying virtual MOs. Strong correlation effects are observed for the levels in the inner valence region where the satellites derive their intensity both from the 2a 1 and 3a 1 MOs.

Theoretical studies of photodissociation and rydbergization in the first triplet state (3s3A″2) of ammonia

Abstract Ab initio investigations at the RHF and CI levels have been carried out on a section of the potential energy surface of the Rydberg 3s 3 A″ 2 state of NH 3 leading to dissociation into NH 2 ( 2 B 1 ) and H( 2 S). It was found that the barrier towards dissociation is due to a Rydberg-valence transformation. The barrier height calculated with the CI wavefunction is significantly smaller than at the RHF level The results may explain the difficulties associated with experimental observation of the 3s 3 A″ 2 state.

Theoretical and experimental studies of the valence photoelectron spectrum of C2H2

A high resolution ESCA spectrum of C2H2 was recorded using monochromatized AlKα excitation and was analyzed by means of configuration interaction and multiple configuration SCF wave functions. The role of different schemes for electron‐configurational selection in the initial and final states on transition moments and energies was investigated. The spectrum shows a prominent satellite structure in the inner valence region, which is analyzed and discussed in terms of electron correlation, dissociative photoionization, interference, and vibronic coupling effects.

Ab initio studies of the photodissociation in the first excited states of à 1A1 and ã 3A1 of PH3

HF and CI calculations were carried out to explain the predissociation process in the first excited A 1A1 state of PH3 that is observed experimentally. It is found that the mechanism of the predissociation involves Rydberg‐valence transformation leading to the production of PH2(X 2B1, A 2A1) and H(2S). This process is similar to that found in the first excited 1A2′′ state of NH3; however, the thermodynamics of the two processes are different. A corresponding study for the PH3(a 3A1) reveals a major difference from the 3A2′′ of NH3 due to the absence of the Rydberg character of the PH3(a 3A1) at the equilibrium geometry. In addition, we report HF calculations on the equilibrium bond distances and the angles, the vibrational frequencies and the barriers to inversion of the neutral ground state of PH3(X 1A1), its first singlet and triplet excited states (A 1A1 and a 3A1, respectively), and the ground state ion (X 2A1).

Multielectron transitions in the K-shell electron energy loss spectrum of N2

Abstract Ab initio investigation on the role of multielectron transitions in the discrete and near continuum parts of the K-shell electron energy loss spectrum of N 2 are reported. An explanation for observed fine structure in the continuum is suggested.

Core Level Shifts in Transition Metal Compounds

Ab initio SCF calculations of X-ray emission chemical shifts are presented for the molecules TiH4, TiH3F, TiF4, and TiF2. The calculated Ti Kα1,2 shifts parallel 3d orbital populations through a coupling via the radial extension of the 3p and 3s orbitals. Anomalous results are obtained for TiF2, which was calculated in a closed-shell configuration differing from its ground state. Potential models for chemical effects in core level spectra are shown to violate the atomic virial theorem but have still value as semiempirical tools.

Calculation of vibrational structure in the core and valence esca spectra of CO and N2

Abstract The vibrational excitations in the core and valence ESCA bands of CO and N 2 have been investigated by means of Franck—Condon (FC) analysis. FC factors obtained from optimized geometries and from the force constants of the neutral ground and ionized states are compared with those obtained from calculated ionized-state energy gradients. Geometries, force constants, and energy gradients are calculated both from frozen-orbital energies and from OS RHF wavefunctions. The differences between the results of the methods employed are discussed in the light of experimental data.

Role of Core Hole State Geometry in Molecular Electron Spectroscopies

The concepts of bonding and antibonding orbitals [1, 2, 3] have played an important role in the qualitative understanding of molecular electronic spectra. This characterization of orbitals was thought to be reserved for valence electron spectra in the UV of optical energy regions, whereas the core orbitals were attributed to a strictly non-bonding function in the formation of the molecule due to their negligible overlap with orbitals of neighboring atoms. This view was also believed to find support in early theoretical investigations indicating only a minor dependence of the core orbital functions on different nuclear configurations.

Vibrational Excitation in ESCA and Soft X-ray Emission Spectra of Small Polyatomic Molecules

The vibrational envelopes of the core ESCA bands of H2O and NH3 and of the 3a1 X-ray emission band of NH3 have been investigated by means of Franck-Condon analysis. The data for the equilibrium geometry and the force constants of the neutral ground, N1s and 3a1 ionized states of NH3 have been computed from ab initio wave functions, whereas the data for the neutral ground and the O1s state of H2O have been taken from literature [1]. The N1s state of NH3 is found to be planar with a significantly shortened N-H bond length in comparison with the neutral ground state. The ionization of the O1s state of H2O leads to an increase of the HOH angle by ~ 16° with negligible change in the O-H bond distance. The vibrational intensities and energies computed from the ab initio results explain the band profiles of the spectra.