Fragment Molecular Orbitals for Molecules and Interacting Systems

Different approaches to describe the structure and properties of molecules as well as reactions between molecules in terms of localized fragment orbitals and their interactions are briefly reviewed and the method of fragments-in-molecules (FIM) is delineated: The FIM method is formulated entirely in terms of strictly transfera< ble fragment orbitals (FO\u27s) which makes it possible to reduce the basis set in order to simplify the calculations, to save computer time and to make the results even more visual. Calculations within the CND0/2 approximation on CH3-S molecules with S = CH3, NH2, OH, F, CN, CH=CH2 and CH=O are used to demonstrate the effect of limiting the number of virtual orbitals taken into account and to an<l\u27lyse inductive and mesomeric interactions. It appears that the same orbital interactions between occupied and virtual FO\u27s of different fragments which are responsible for the rotational barrier also have the largest effect on the total energies of the systems under consideration. A partitioning of the energy of interaction between molecular fragments based on the formulation of the FIM approach yields definitions of inductive and mesomeric effects which are in good accord with chemical experience and is closely connected with other energy partitioning schemes

Fragment Molecular Orbitals for Molecules and Interacting Systems

Different approaches to describe the structure and properties of molecules as well as reactions between molecules in terms of localized fragment orbitals and their interactions are briefly reviewed and the method of fragments-in-molecules (FIM) is delineated: The FIM method is formulated entirely in terms of strictly transfera< ble fragment orbitals (FO\u27s) which makes it possible to reduce the basis set in order to simplify the calculations, to save computer time and to make the results even more visual. Calculations within the CND0/2 approximation on CH3-S molecules with S = CH3, NH2, OH, F, CN, CH=CH2 and CH=O are used to demonstrate the effect of limiting the number of virtual orbitals taken into account and to an<l\u27lyse inductive and mesomeric interactions. It appears that the same orbital interactions between occupied and virtual FO\u27s of different fragments which are responsible for the rotational barrier also have the largest effect on the total energies of the systems under consideration. A partitioning of the energy of interaction between molecular fragments based on the formulation of the FIM approach yields definitions of inductive and mesomeric effects which are in good accord with chemical experience and is closely connected with other energy partitioning schemes

Finite Size Effects in Fluid Interfaces

It is shown that finite size effects in the free energy of a rough interface of the 3D Ising and three--state Potts models are well described by the capillary wave model at {\em two--loop} order. The agreement between theoretical predictions and Monte Carlo simulations strongly supports the idea of the universality of this description of order--order interfaces in 3D statistical systems above the roughening temperature.Comment: 3 pages, uuencoded .ps file, figures included. (Proceeding of Lattice '93

Rough Interfaces Beyond the Gaussian Approximation

We compare predictions of the Capillary Wave Model with Monte Carlo results for the energy gap and the interface energy of the 3D Ising model in the scaling region. Our study reveals that the finite size effects of these quantities are well described by the Capillary Wave Model, expanded to two-loop order (one order beyond the Gaussian approximation).Comment: Contribution to LATTICE 94. 3 pages, PostScript fil

The Fragments-in-Molecules Method Ill. Inductive and Mesomeric Effects

Within the framework of the recently developed FIM method the interaction of FO\u27s is evaluated in two steps: inductive perturbations are calculated on the basis of the generalized product approach treating each fragment in the field of all other fragments. The mesomeric interactions in the composite system are then obtained from SCF calculations based on these FO\u27s. Applications to re systems based on the PPP approximation as well as applications based on the CND0/2 approach show that this definition of inductive and mesomeric effects is quite natural and useful in discussing the electronic structure of organic molecules

Finite-Size Effects in the Interface of 3D Ising Model

The interface between domains of opposite magnetization in the 3D Ising model near the critical temperature displays universal finite-size effects which can be described in terms of a gaussian model of capillary waves. It turns out that these finite-size corrections depend rather strongly on the shape of the lattice. This prediction, which has no adjustable parameters, is tested and accurately verified for various lattice shapes by means of numerical simulations with a cluster algorithm. This supports also a long-standing conjecture on the finite-size effects in Wilson loops of Lattice Gauge Theories.Comment: 13 pages, plain latex, two figures not included, sorry DFTT 68/9

Interface Tension of the Electroweak Phase Transition

In our nonperturbative lattice investigation we study the interface tension of the finite-temperature electroweak phase transition. In this analysis the Higgs mass has been chosen to be about $35$ GeV. At the transition point of a finite volume system, tunnelling between the symmetric and the Higgs phase takes place. This phenomenon leads to a splitting of the ground state, which can be used to determine the interface tension. The result obtained this way agrees with the result of the two-coupling method and with the prediction of the perturbative approach.Comment: 10 pages, five figures in uuencoded PS format, Latex + epsf.st

Electronic spectroscopy of 9,10-dichloroanthracene inside helium droplets

The spectroscopy of molecules doped into superfluid helium droplets provides information on both, the dopant molecule and the helium environment. Electronic spectra of 9,10-dichloroanthracene in helium droplets are presented and compared with corresponding gas phase spectra to unravel the influence of the helium environment. The combined investigation of fluorescence excitation and dispersed emission provides information on dynamic processes in addition to energetic conditions. For vibronic states, the helium induced decay channels dominate over all intramolecular channels that contribute to the gas phase behavior. In addition to the triplet splitting caused by the Cl isotopes, a fine structure resolved for all transitions in the fluorescence excitation spectrum was found, which is the signature of microsolvation of this compound in helium droplets. This fine structure is identified as a single pure molecular transition accompanied by a sharply structured phonon wing. The corresponding fine structure measured for bare anthracene shows remarkable differences

Ein neues, unkompliziert auszuführendes Verfahren zur Bestimmung kleiner Konzentrationen an Wasser in organischen Lösungsmitteln

A new procedure for the determination of water (even in trace amounts) in organic solvents is described. The solvatochromism of the pyridiniumphenol betaine, E T30, determined by a simple UV-absorption measurement, together with a two-parameter equation, permits an exact determination. The procedure is rapid and is, therefore, an alternative to the Karl-Fischer titration

Bestimmung der Zusammensetzung binärer Flüssigkeitsgemische mit Hilfe von Fluorescenzmessungen

A simple procedure for the determination of water in organic solvents and more generally of the composition of binary liquid mixtures by use of solvatochromic fluorescent dyes is described even for samples with low transparency. The procedure can be carried out without any spectrometer using only an array of optical filters