No abstract

No abstract

No abstract

The energies of the three lowest lying excited states of the ozonide anion (1 2B2, 1 2A1, 1 2A2) at the optimized geometry of the X 2B1 ground state are theoretically predicted at the MRCI-SD level of theory using large atomic natural basis sets. The calculated vertical excitation energy Tv=2.85 eV for the 1 2A2←X 2B1 transition, which has a large transition moment, is in good agreement with the experimental results for the isolated O3− anion in host matrices and solution between 2.69–2.81 eV. The state symmetry forbidden transition 1 2B2←X 2B1 is calculated with Tv=2.26 eV. The excitation energy for the 1 2A1←X 2B1 transition is theoretically predicted with Tv=2.28 eV and a very low transition moment. The theoretical results are also discussed in comparison with recently observed low lying absorption bands of O3−.

Abstract. Synthetic orthopyroxenes free of trivalent cations MgxFez -xSi206 (x = 0; 1; 1.6) were investigated using both M6ssbauer spectroscopy (MS) and single-crystal X-ray diffraction (XRD) in order to compare the results obtained on the same samples by the two techniques. The Mg-Fe distribution over M1 and M2 octahedral sites was determined on compounds with x = 1 and x = 1.6, unheated and annealed at 650, 850 and 1040 ~ C for 29 to 42 hours to obtain different degrees of order. The data obtained by the two techniques are in very good agreement, thus suggesting, for these compositions, the absence of systematic errors. The investigation of a synthetic compound with x=0 (ferrosilite) confirmed that the accuracy of both methods is very good. The observed small discrepancies between the results are not significant if compared with the relevant standard deviations which, for both methods, were derived by leastsquares calculations. The best fit is obtained for Fe(M1)/ Fe(tot) parameters that, in both methods, are directly calculated without using data from chemical analysis. For the unheated samples the values by MS and XRD are respectively: 0.185(9) and 0.180(4) for x = 1.6; 0.282(8) and 0.285(2) for x=l; 0.503(7) and 0.502(1) for x=0. For all the investigated samples the correlation between the geometrical distortion parameters, calculated by Xray refinement, and the quadrupole splitting values, measured by M6ssbauer spectroscopy, agrees with the theoretical model of Ingalls (1964).