Zur Konzentrationsabhängigkeit der Elektronenspin-Relaxationszeiten von Diphenyl-Picryl-Hydrazyl in fester Phase

The influence of exchange and dipol interaction on the EPR-relaxation timesT ₁ andT ₂ of DPPH has been measured in theX-band between 295 and 2°K. The spinconcentration has been varied between 1.5·10²¹ spins/cm³ (single crystals) and 1.5·10¹⁸ spins/cm³ (solid solution in polystyrene). The EPR absorption was saturated stationarily. This gave the productT ₁ T ₂ from the saturation curve and the timeT ₂ from saturation broadening of the absorption spectrum.     

Singular unitary representations and indefinite harmonic theory

Square-integrable harmonic spaces are defined and studied in a homogeneous indefinite metric setting. In the process, Dolbeault cohomologies are unitarized, and singlar unitary representations are obtained and studied.     

Orientation of anthracene molecules in naphthalene single crystals

The orientation of anthracene in naphthalene matrix has been determined by EPR of the triplet state of the guest molecule. It differs from the host molecule orientation mainly by a rotation of 25° about the z axis.     

Efficient methods for configuration interaction calculations

Advanced techniques are developed to provide efficient economic treatment of the large scale eigenvalue problem posed when configuration interaction is carried out on SCF basis sets of moderate size. When the characteristic properties of the hamiltonian matrix are examined in light of the type of solution required, partitioning of the configuration space is shown to result in an expansion of the problem about a limited core of states, where the small but cumulative interactions of vast regions of the remaining space are reduced to the form of an effective potential. With proper selection of the core, the evaluation of this potential can be readily and accurately truncated to a level involving minimum expenditure in time and effort. In particular only diagonal elements and a strip of the full CI matrix are required to achieve an accuracy of 1 – 5 kcal/mole with complete treatment for configuration spaces of order tens of thousands. In addition, a close look at current theory on the generation of matrix elements between spin symmetry adapted configurations leads to simplified expressions where the matrix elements are derived in the form of a weighted sum of molecular integrals in which the weighting coefficients represent the integrated value of the wavefunctions over spin coordinates. For typical cases of low multiplicity and limited numbers of open shells the list of unique parameters needed to generate all weights are shown to be readily stored as a program library. Actual times for matrix element generation are believed to be an order of magnitude faster than current techniques. Practical demonstration of the accuracy and efficiency of the method is provided by calculations on formaldehyde, water, and ethylene.     

Phosphoranes bicycliques a liaison PH : Bases de Lewis potentielles

By reaction of Borane Dimethyl Sulfide on the bicyclophosphorane $\text{1}$ the adduct $\text{2}$ is obtained with 56 % yield; by-products $\text{3}$ and $\text{4}$ are characterized .