Oscillator strengths, semiempirical calculations

Figure 12. Electronic spectra and the results of open-shell PPP-like semiempirical calculations for radical ions. The vertical lines represent the allowed transitions, the wavy lines with arrows the forbidden ones. The right side scales denote the calculated spectral intensities, where f stands for the oscillator strength. Top left the absorption curve (146) redrawn to the log e vs. 0 (cm ) form calculations are taken from (59). Top right taken from (11). Bottom left taken from (143). Bottom right taken from (136), the absorption curve redrawn to the log e vs, 0 (cm" ) form.

Figure 14. Absorption curves of the tetracene radical ions (157) and results of the semiempirical open-shell PPP-like calculations (59). The latter are indicated by vertical lines (allowed transitions) and by wavy lines with arrows (forbidden transitions) f stands for theoretical oscillator strength.

The electron densities, bond orders, first six excitation energies, oscillator strengths, and weighting factors of pyrido[l,2-f)]pyridazinium cation were calculated by the PPP semiempirical version of the SCFMO-CI method, which indicated that protonation is expected to take place at the nonbridgehead nitrogen, and nucleophilic substitution is predicted to occur at position 3 (68TCA417i... 

Two semiempirical approaches are commonly applied in calculating the energies and intensities of f-f transitions in rare earth ions. The most common is the so-called Judd-Ofelt method. At this level of theory, the total oscillator strength for an f-f transition between SL/) and S L J ) multiplets is given by Eq. (27) [34,35] ... 

Abstract. We have calculated the scalar and tensor dipole polarizabilities (/3) and hyperpolarizabilities (7) of excited ls2p Po, ls2p P2- states of helium. Our theory includes fine structure of triplet sublevels. Semiempirical and accurate electron-correlated wave functions have been used to determine the static values of j3 and 7. Numerical calculations are carried out using sums of oscillator strengths and, alternatively, with the Green function for the excited valence electron. Specifically, we present results for the integral over the continuum, for second- and fourth-order matrix elements. The corresponding estimations indicate that these corrections are of the order of 23% for the scalar part of polarizability and only of the order of 3% for the tensor part... 

The electron densities, the bond orders, the first six energies, and the oscillator strengths of the pyrido[l,2-c]pyrimidinium cation were calculated using the SCFMO semiempirical version of the PPP method. Protonation is expected to take place on the nonbridgehead N atom, and position 1 is predicted to be most reactive toward nucleophilic substitution (68TCA417). 

The CIS approximation is used in a majority of semiempirical SCF methods to calculate energies and oscillator strengths of electronic transitions (CNDO/S, INDO/S, CINDO-E/S, NDDO/MC, NDDO-G). 

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