Volume 45, Issue 6

Two-step sequential and unistep, superexchange primary electron transfer form primary radical pair states which differ in the direction and magnitude of their dipole moments as revealed in the X-ray structure analysis. The direction can be measured by the excitation anisotropy of electric field induced changes of the fluorescence yield. This method determines angles between the dipole of the primary radical pair and photoselected transition moments (in absorption and emission) of cofactors in the reaction centers. Transitions particularly favourable for discrimination between the two models of primary electron transfer are discussed.

The luminescence spectra and radiative lifetimes of a series of d 3 and d 6 double complex compounds with bipyridine (bip), phenanthroline (phen), ammonia and ethylenediamine (en) ligands in the cations and chloride, cyanide, thiocyanide and oxalate (ox) ligands in the anions have been investigated at temperatures down to 2 K. Although energy transfer between the component ions is predicted from the Förster and Dexter theory to be effective due to the finite overlap of the donor emission and the acceptor absorption spectra, no emission could be detected for most of the double complexes. Only [Ru(bip)3]tr-[Cr(NH 3 ) 2 (NCS) 4 ] 2 , [Ru(bip) 3 ][PtCl 6 ] and [Cr(d 4 -en) 3 ] [Rh(SCN) 6 ] exhibit characteristic luminescence spectra which in part are enhanced compared to their component emissions. For rationalizing the results, radiationless deactivation by various decay channels which compete with the energy transfer mechanism must be considered.

Using the Gaussian effective potential approach, φ 6 soliton solutions at finite temperature are studied for both the general case and the particular case λ 2 = 2ξm 2 . A critical temperature is found at which soliton solutions cease to exist. The effective potential together with the mass-gap equation are studied in detail, and comparison with existing work on this subject is made

Nematic liquid crystals exhibiting a negative K 2 elastic constant are discussed on the basis of a microscopic model potential. Stability conditions are satisfied by taking into account higher order terms in the expansion of the free energy. A continuous Freederiks effect is predicted for systems with negative K 2 .

Physical properties of stoichiometric and non stoichiometric CuO are reported. The electrical conductivity has been measured on CuO pellets, sintered with the usual procedure for the preparation of Y Ba-Cu O superconductors and then deoxygenated under a nitrogen flow. It is shown that oxygen deficient CuO pellets present abrupt and large resistivity drops as the temperature decreases below 230-200 K. Possible correlations between the electrical instability of oxygen deficient CuO and the high temperature superconductivity problem are discussed

A study of the spin-orbit interaction between the A 1 Σ u + and b 3 Π u states of Na 2 , based on the collision-induced transitions (2) 1Σ g →A 1 Σ u + recorded with a high resolution Fourier transform spectrometer, had led to the determination of the deperturbed constants of the A 1 Σ u + and b 3 Π u states [1]. From these constants the Rydberg-Klein-Rees (RKR) potential curves for the A 1 Σ u + (0≦v≦ 15) and b 3 Π u (0 ≦ v ≦ 25) states and the Franck-Condon factors (FCF) within the range of vibrational levels involved in the interaction of these two states are calculated, together with the mixing coefficients for the pair (A 1 Σ u + ) v=4 - (b 3 Π u ) v=10 .

MINDO-forces calculations have been done after complete optimization of geometry on X-monosubstituted fulvenes, where X is OH, NH 2 , CH 3 , NO 2 , CN, F, dimethyl and cyclopropyl. It was found that all the substituents are stabilizing. The electron releasing substituents increase the dipole moment at the exocyclic double bond while the electron withdrawing ones increase the dipole moment at the endocyclic diene. Geometrical parameters, heats of formation, orbital energies and electron densities are reported.

We reinvestigated the rotational spectra of tert-butyl bromide (CH 3 ) 3 C 79 Br and (CH 3 ) 3 C 81 Br, with the high precision of microwave Fourier transform spectroscopy. The rotational and quadrupole coupling constants were improved, the centrifugal distortion and bromine spin-rotation constants were determined

We reinvestigated the rotational spectrum of perchlorylfluoride- 35 Cl and - 37 Cl by microwave Fourier transform spectroscopy and determined the rotational, centrifugal and quadrupole coupling constants and the dipole moment with higher precision and the spin-rotation constants for the first time.

Higher molecular polycyclic aromatic hydrocarbons (PAH) form supersaturated solid solutions in perhydrocoronene. With coronene as the solute, concentration-dependent P-type delayed fluorescence is observed at 77 K. Even very small amounts of coronene, present as an impurity in the perhydrocoronene matrix, can lead to quenching of the phosphorescence of an added guest PAH by intermolecular triplet-triplet energy transfer and to sensitized coronene phosphorescence when the lowest triplet state of the added guest molecule lies higher in energy than that of coronene. Thermal band broadening of guest molecule phosphorescence has been studied in the temperature range from 77 to 433 K.

A high resolution study of the rotational spectrum of formaldoxime was carried out with the aim to resolve a discrepancy between early microwave results and recent ab initio calculations. Accurate 14 N quadrupole coupling constants and spin-rotation coupling constants could be derived from zero field hfs multiplets. From the Zeeman-splittings in external magnetic fields up to 18kGauss the diagonal elements of the molecular g-tensor and the anisotropics in the diagonal elements of the molecular magnetic susceptibility tensor were obtained and were used to derive the diagonal elements of the molecular electric quadrupole moment tensor. For comparison, Hartree Fock SCF calculations were carried out with a basis of TZVP quality. As it turned out such calculations are able to reproduce the molecular electric quadrupole moment tensor but fail to reproduce the 14 N nuclear qudrupole coupling constants to better than 0.3 MHz. A revised formula to predict spinrotation coupling constants of first row elements such as nitrogen is also proposed.

Internal cation mobility ratios in molten (Li, Pb(II))Cl at 650 °C have been remeasured by Klemm's column method. From these and available data on the densities and conductivities, the internal mobilities b Li and b Pb have been calculated. It was found that at low LiCl content bu is surprisingly high, while at low PbCl 2 content b Pb is surprisingly low. The former trend agrees with that found by Klemm and Monse with the migrating boundary method and disagrees with that found by Behl and Egan with the EMF method. The latter trend agrees with that resulting from a neglected point given by Behl and Egan and disagrees with that tentatively reported by Klemm and Monse. The peculiar mobility behaviour of (Li, Pb(II))Cl is compared with that of similar Cd(II), Sr, and Ba systems

The ionization current produced in liquid tetramethyl germanium by 60 Co-γ-radiation was measured with a guard ring type, parallel plate ionization chamber. The yield of ion pairs as a function of the applied electric field strength was determined and the free ion yield without applied electric field was obtained to be G fi (0) = 0.68 ±0.10.

We have investigated the dynamical behavior of p-Ge at the very onset of impact ionization breakdown. The statistical temporal distribution of the recurrent breakdown events exhibits a power law behavior supporting the model of selforganized criticality introduced by Bak, Tang, and Wiesenfeld.

The pure rotational spectrum of NNO has been observed as an impurity in the NO spectrum which has been recorded with a high resolution Fourier transform spectrometer. The observed high-J transitions in the ground vibrational state were analyzed by a least-squares fit together with the available millimeter and submillimeter wave data. It has been proved that the highly precise data of Maki et al. [3] can be used as a wavenumber standard for the far infrared.