The electronic structure of poly(pyridine-2,5-diyl) investigated by soft x-ray absorption and emission spectroscopies

The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and nonresonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the {\pi} electron bands in line with symmetry selection and momentum conservation rules. The effect is most vizual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of {\sigma} symmetry and are less frequency dependent.Comment: 11 pages, 7 figures, 1 table, http://www.sciencedirect.com/science/article/pii/S030101049800262

AUTOIONIZATION OF CO AFTER C ls-+2rc* EXCITATION: A COMPARISON WITH PHOTOEMISSION AND AUGER DECAY

We have calculated the entire autoionization spectrum of CO following core-to-bound, i.e. C ls+2x* excitation, within a Green's function formalism. Approximate autoionization transition intensities can be related to the Hamiltonian matrix elements. Initialstate screening is important for obtaining realistic autoionization probabilities. For the low-lying ion states there is a one-to-one correspondence between the photoelectron and the autoionization spectrum, The connection between autoionization and Auger decay is discussed

(AmBn)x copolymers: A computational study of electronic and excitonic properties of quasi-one-dimensional superlattices

Periodic copolymers representing quasi-one-dimensional superlattices (AmBn)x have been studied within the tight-binding approximation. The linear-combination-of-atomic-orbitals (LCAO) approach was used to calculate the splitting into subbands, the widths of the subbands, and the number of subbands in the well as a function of segment lengths m and n (barrier and well width). The Stark shift of subbands and the perturbed Wannier functions for a (A16B32)x superlattice have been calculated for various electric field strengths using perturbation theory. Exciton resonances and the shift in exciton excitation energies due to an applied electric field have been computed by using a Pariser-Parr-Pople parameter for the electron-hole interaction. The parameters for the empirical tight-binding calculations were determined from fully self-consistent Hartree-Fock calculations and first-principles Greens function calculations for the exciton energies for superlattices of shorter segment lengths. For the Stark shift of the exciton peak a red shift of 25 meV for 2×105 V/cm is calculated, similar to the shifts calculated and observed in three-dimensional superlattices. © 1988 The American Physical Society

Electronic states of poly(thiophene-isothianaphthene) superlattices

The density-of-states curves of periodic and non-periodic poly(thiophene-isothianaphthene) block-copolymers of different composition have been calculated by the negative-factor-counting method. A discussion of the trends in band-gap variation is given. © 1989

Matrix elements of Lorentzian Hamiltonian constraint in loop quantum gravity

The Hamiltonian constraint is the key element of the canonical formulation of loop quantum gravity (LQG) coding its dynamics. In Ashtekar-Barbero variables it naturally splits into the so-called Euclidean and Lorentzian parts. However, due to the high complexity of this operator, only the matrix elements of the Euclidean part have been considered so far. Here we evaluate the action of the full constraint, including the Lorentzian part. The computation requires heavy use of SU(2) recoupling theory and several tricky identities among n-j symbols are used to find the final result: these identities, together with the graphical calculus used to derive them, also simplify the Euclidean constraint and are of general interest in LQG computations