Jelena Radić-Perić

Ab initio investigation of the Renner effect in the C3 molecule

Abstract A method is developed for the ab initio treatment of the coupling between the electronic and vibrational motions in triatomic molecules. It is based on a polynomial expansion of the molecular potential and the use of a variational method for calculations of vibronic wavefunctions. The results for the 1 H u state of the C 3 molecule are reported.

Spectroscopic Investigation of Direct Current (DC) Plasma Electrolytic Oxidation of Zirconium in Citric Acid

Plasma electrolytic oxidation of zirconium in citric acid was investigated using optical spectroscopy. A rich emission spectrum consisting of about 360 zirconium and 170 oxygen atomic and ionic lines was identified in the spectral regions 313–320, 340–516, and 626–640 nm. It was shown that the remaining features observed in the spectrum could be ascribed to various molecular species, which involve zirconium, oxygen, hydrogen, and carbon. The temperature of the plasma core (T = 7500 ± 1000 K) was determined using measured Zr line intensities, and the temperature of peripheral plasma zone (T = 2800 ± 500 K) was estimated from the intensity distribution within a part of an OH spectrum. The composition of the plasma containing zirconium, oxygen, and hydrogen, under assumption of local thermal equilibrium, was calculated in the temperature range up to 12 000 K and for pressure of 105 and 107 Pa, in order to explain the appearance of the observed spectral features.

The anomalous sodium doublet D2/D1 spectral line intensity ratio – a manifestation of CCD's presaturation effect

In this paper we present the results of intensity measurements of D1 (589.5224 nm) and D2 (588.9950 nm) sodium doublet spectral lines emitted from a short-lifetime plasma randomly appearing across the aluminum anode surface during its electrolytic oxidation from the water solution of boric acid with sodium tetraborate. We found that the D2 to D1 intensity ratios were not constant, varying from 2 to 1.2. Assuming that the plasma is in local thermal equilibrium it is expected that the intensity ratio of sodium doublet components equals the ratio of the statistical weights of the atomic sublevels corresponding to the electronic transitions (D1: 32P1/2–32S1/2, D2: 32P3/2–32S1/2) i.e. 2. After detailed analyses of a series of spectra obtained by applying different detection parameters, like exposure time, slit width, detection mode, and number of accumulations, we attributed the anomalous D2/D1 intensity ratio to the effect of approaching a saturation condition of the charge coupled device detector and thus to an early indication of saturation occurrence.

Thermodynamical modeling of silicon carbide synthesis in thermal plasma

The synthesis process of solid SiC in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixtures involving silicon and carbon in the presence of argon and hydrogen at various silicon/carbon amounts and at two different total pressures in the system, in the temperature range between 1000 and 6000 K. Use is made of the fact that a thermal plasma, by definition, is a plasma in (local) thermodynamical equilibrium, which makes possible the theoretical determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds present in the system. From the calculated compositions of the investigated gas systems the temperature-composition phase diagrams were obtained. Using these data the temperature zones with saturated and/or oversaturated vapour of SiC as well as of Si and C were determined and the possibility of the formation of SiC in the solid state via different reaction routes was analyzed

Ab initio investigation of the vibronic structure and the spin–orbit coupling in the X2Πu state of C2D2+

Results of an ab initio study of the Renner–Teller effect in the X2Πu state of C2D2+ are presented. Potential curves for the trans- and cis-bending vibrations calculated by means of the internally contracted multireference configuration interaction method are employed. Vibronic energy levels and their splitting upon spin–orbit coupling are computed by means of a variational approach.

Boron, calcium and silicon in an arc plasma in air with chlorine: calculation of the plasma composition

The composition of an air plasma in the presence of chlorine (0.1%), and boron, calcium or silicon (at concentrations in the plasma of 0.0001%), was calculated assuming thermal equilibrium, in the temperature range 298–6000 K. The calculated plasma composition reproduces the composition of the d.c. arc plasma free burning in air, as the plasma is assumed to be in (local) thermal equilibrium. Assuming that an arc is usually operated between graphite electrodes, the presence of carbon in the plasma (1%) was also taken into account. It was found that the presence of chlorine in the plasma caused a decrease in the atomic, ionic and molecular forms of calcium, boron and silicon and their spectral line and band intensities (compared with observations in the absence of chlorine) only at temperatures <3000 K. The presence of carbon in the plasma (under the conditions investigated) had almost no influence on the partial pressures of calcium, boron and silicon species and on the partial pressures of compounds of chlorine with oxygen and nitrogen. Also, the change in partial pressures of CN, C2etc.(the radiation of these molecules produces the background band spectra in the graphite arc), in the presence of chlorine, cannot be observed.

Evaluation of Partition Functions of Triatomic Molecules Using Data Obtained by ab initio Calculations — Sums of States of Molecules with Spatially Degenerate Lowest Electronic States

The evaluation of partition functions of triatomic molecules based on data obtained by means of the ab initio method is discussed. Special attention is paid to molecules exhibiting the Renner- Teller effect. Various approximate approaches for the calculations of partition functions are explicitly considered. The results are shown for HNF, NCO and BH2.