Nada Orlić

Inductive effects in alternants hydrocarbons: the two-photon spectra of biphenylene and 2,3,6,7-tetra-ethyl-biphenylene

Abstract The two-photon spectra of biphenylene (BP) and 2,3,6,7-tetra-ethyl-biphenylene (TEBP) have been measured in the region of the lowest two electronic transitions (310–440 nm). The S 0 → S 1 transition of BP, although group-theoretically allowed, is only weakly observed. The TEBP spectrum is, for both transitions, stronger than that of BP. The experimental data are related to the pseudoparity symmetry of altemant hydrocarbons and to the inductive perturbation of pseudoparity selection rules. Due to the enhancement, the TEBP spectrum shows additional spectral structures with respect to BP, among which is the weak onset of the S 0 → S 1 transition around 23100 cm −1 .

Mechanism for nuclear excitation during positron annihilation using Coulomb wave functions

Abstract We have calculated cross sections for the process of nuclear excitation during positron annihilation on any bound electron. We used Coulomb wave functions for the electron and positron.

Nuclear excitation by positron annihilation with bound electrons in a screened atomic potential

Abstract We have calculated the total cross section for the process of nuclear excitation in positron-bound electron annihilation. The calculations presented in this work use a spherically symmetric screened atomic potential. Comparisons with more approximate treatments of the process are made.

Elemental analysis of archaeological objects by X-ray emission spectroscopy

In our measurements on samples, characteristic X-rays induced by a radioactive Cd-109 source were deteced in a high resolution Si(Li) detector. In the current experimental arrangement, it is possible to detect X-rays in the interval of energy 2-20 keV. All samples have been analyzed under the same conditions. The elemental composition of two leaden seals from the Republic of Ragusa were measured. Quantitave spectrum analyses showed that in the leaden seals there is gallium and iron in addition to the lead, which is the dominant element. Concentration of bizmuth, gold and selenium were found to be within the detection limit. Metal content, with the exception of silver, have also been measured in two ancient and two medieval silver coins.

Angular correlation of double internal bremsstrahlung in the electron capture decay of 55Fe

Abstract The angular correlation of photons emitted in double internal bremsstrahlung (DIB) associated with the electron capture (EC) decay of 55 Fe has been investigated. Relative emission angles ranged from 50° to 150°. Photons from the 1 mCi source were detected in two 5 cm × 5 cm diameter NaI(Tl) counters; the sum energies of photons was in the range of 68–231 keV. Experimental results were compared with the theoretical predictions for 1s, 2s, 2p and 3p initial electron state contributions.

Vibrational relaxation of three-phonon bound states in crystal CO2

Abstract Vibrational lifetimes of three-photon bound states (triphonons) observed in the vibrational region 3ω2;(ω1 + ω2) of crystal CO2 have been measured in the temperature range 10–200 K. The relaxation is interpreted in terms of depopulation of excited levels and dephasing by low-frequency phonons. A comparison with results for biphonons in the Fermi resonance region 2ω2;ω1 is made and similarities are discussed.