Erik W. Thulstrup

Configuration interaction calculations of low‐lying electronic states of O2,O2+, and O22+

Minimal basis full valence CI calculations of potential curves are reported for more than 300 low‐lying states of O2, O+2, and O2+2. A large number of new bound states of O+2 and some metastable states of O2+2 are predicted, and from a comparison with known states of O2 and O+2, predictions are made for the spectroscopic constants of the as yet experimentally unknown states.

Configuration interaction calculations of some observed states of NO−, NO, NO+, and NO2+

Minimal STO basis has been used in configuration interaction calculations on the molecule NO and some of its ions. Several observed states of these systems have been calculated with full potential energy curves, and comparisons have been made with results from photoelectron spectroscopy, double charge transfer spectroscopy, and photodetachment spectroscopy.

Elementary Excitations in a Benzene Model

A two‐parameter model for the π electrons in the benzene molecule is examined in detail by the method of complete configuration interaction and the results are used for a comparison with an approximate propagator or Greens function technique applied to the model. It is demonstrated that the approximate method gives a qualitatively nearly correct description of the electronic structure for a range of parameter values which simulate the limits of separated atoms and of small electronic interaction. The quantitative comparison is generally better than what is possible with the molecular orbital method.

The electronic structure of p-terphenyl, 3,6-diphenyl-pyridazine and 3,6-diphenyl-s-tetrazine

Photoelectron spectroscopy, polarized electronic absorption spectroscopy in stretched polymer sheets, and several semi-empirical theoretical methods have been applied in an investigation of the valence electronic structures of the three title compounds. Overall consistency between theory and experiment has been obtained by assuming an effectively planar molecular structure. Large MCD B-terms are predicted for the two lowest π-π* transitions in the two aza-compounds.

Polarized spectroscopy of partially oriented molecules. A general formulation for two‐photon processes in uniaxial samples

General expressions are given for linearly polarized intensity in a two‐photon experiment on a uniaxial assembly of partially aligned molecules of arbitrary shape and symmetry, without any assumptions concerning the detailed nature of the uniaxial orientation distribution. The formulas are valid for electric dipole interactions and apply to measurements such as ordinary and resonant Raman scattering, two‐photon absorption, photoluminescence, and transient or permanent photoinduced dichroism measured in stretched polymers, nematic liquid crystals, or lipid bilayers. Two examples are worked out in some detail: nonresonant Raman scattering and photoluminescence of symmetrical molecules. A discussion of the physical significance of the orientation factors and of their interrelation is given.

The momentum distribution in some electronic states of the neutral and singly ionized nitrogen molecule

Abstract Momentum densities for the N 2 molecule are investigated. Differences between the ground state and low-lying excited states as well as the effects of ionization are discussed. The densities are calculated by taking Fournier transforms of natural spin orbitals of wavefunctions calculated in a minimal basis with configuration interaction.

The electronic structure of cyclazines

The electronic structure of cyclopenta[h]cycl[4.2.2]azine (1) has been investigated by means of photoelectron spectroscopy and by polarized electronic absorption spectroscopy in stretched polyethylene sheets at 77 K. The measured transitions have been assigned to transitions calculated by a number of semi-empirical methods. The analysis of the results implies that the essential features of the electronic structure of 1 are well described in terms of those of a planar [14]annulene, perturbed by single-bond cross-links.

A theoretical investigation of the low-lying states of the C−2 ion

Abstract Ab initio calculations in the valence shell CI approximation have been carried out for 1Σ+g states of C2 and for doublet and quartet states of C−2 with Σ, Π and Δ symmetry. The results confirm tentative assignments made from experimental studies of the three lowest states of C−2.

Electronic spectra of dithieno analogues of phenanthrene

The magnetic circular dichroism (MCD) spectra of some dithieno analogues of phenanthrene: benzo [2,1-b;3,4-b′] dithiophene (I) benzo [1,2-b;4,3-b′] dithiophene (II), benzo [1,2-c;3,4-c′] dithiophene (III) and benzo [1,2-b;3,4-b′] dithiophene (IV) are reported. For I–III the spectra corresponding to two different transition moment directions could be obtained from low-temperature linear dichroism spectra. The results compare well with theoretical energies, oscillator strengths, moment directions and MCD B-terms which were obtained from semi-empirical quantum mechanical calculations in the π-electron approximation.

Excited singlet states of fluoranthene: Linear dichroism, polarized fluorescence excitation, and anodic oxidation of the aminofluoranthenes

Abstract Transition energies, intensities, and polarization directions have been determined for six to nine transitions in each of the five isomeric aminofluoranthenes, using absorption, polarized excitation and emission, and linear dichroism in stretched polyethylene. Probable error limits for the stretched-sheet method are discussed. Most of the transitions have been further characterized by the sign of the corresponding peak in magnetic circular dichroic spectrum. The low-energy transitions have been correlated with those of fluoranthene. Interesting differences between the isomers are noted. Simple Pariser-Parr-Pople theory accounts well for most observations but predictions of polarization directions of higher-energy transitions are poor. Anodic polarographic oxidation of the five aminofluoranthenes, the six aminobenzo[c]phenanthrenes, and some additional arylamines has been studied, and the relationship to the spectroscopic results noted. A fair correlation has been found between the anodic half-wave potentials of 24 arylamines and the calculated energies of their highest occupied molecular orbitals.