Volume 37, Issue 1

We discuss the integrated form of the laws of thermostatics by using Stokes theorem on manifolds. We give a new insight to the basic properties of thermostatics, in particular we show that only the second law is a necessary condition to identify the integrating factor with the temperature. Moreover we consider the thermodynamical field equations for discontinuous media and discuss the properties of thermostatics.

A study is made of solitary waves propagating along a constant, uniform magnetic field in a warm collisionless plasma. The calculation is based on a two-fluid model of the plasma. It is found that the effect of the thermal motion of ions and electrons is to reduce the amplitude but enhance the velocity of propagation of the solitary wave.

The formation of quasimolecular ions by alkali ion attachment in laser desorption mass spec-trometry has been investigated by using a CW CO 2 laser. For molecules such as sucrose the desorption of preformed ions could be excluded. Evidence is presented for the ionization by alkali ion attachment in the gas phase. Quasimolecular ions of organic salts were found to result from cationization reactions in the gas phase and from surface reactions. Very fast cation exchange reactions have been discovered for salts and acids impinging on alkali ion emitting surfaces.

133 Cs nuclear magnetic resonance has been studied in the solid compound semiconductor Cs 3 Sb between room temperature and the melting point. From the magnitude of the chemical shift (620±25 ppm at 300 K) and the quadrupolar coupling constant {e 2 qQ/h = 105 ± 3 kHz) we conclude that predominantly ionic bonding does not occur in this semiconductor.

Ion formation from alkali halide solids caused by the irradiation of high power (some 10 8 W/ cm 2 ) pulsed lasers is investigated by means of time-of-flight mass spectrometry (LAMMA®). It is shown that the ions are formed directly from the solid state, several uppermost atomic layers being involved; gas phase interactions are negligible. The ion formation rates, however, are in-compatible with the assumption of a quasiequilibrium phase transition, but should be explained in terms of non-adiabatic rate processes discussed in some detail. The light absorption of the transparent halide crystals is assumed to be initiated by multiphoton absorption - free electron production; the further energy transfer being maintained by rapid polaron-Joule-heating. The data are compatible with this model.

It is shown on the grounds of a semiempirical PPP-treatment that for the equidistant eistrans infinite polyene two types of Hartree-Fock solutions are possible-one yielding a cis-transoid and the other a trans-cisoid distribution of nearest-neighbour bond-orders. Relaxing the nuclear framework according to bond-order magnitudes for the bond-alternation wave (BAW) in the equidistant all-trans polyene, resp. for the two solutions for the equidistant cis-trans polyene mentioned above and using repeatedly the Coulson-Golebiewski formula, realistic self-consistent values of bond lengths have been obtained. The calculated energy differences between the investigated isomers are small, predicting almost equal probabilities. The expressions for the PPPwavefunctions are presented in analytical form suitable for further applications. Long-range Coulomb interactions have been accounted for up to convergence of the groundstate energies.

An analytical solution to the Wigner-Weisskopf problem (an excited two-level atom in inter-action with a radiation field), obtained for both finite-and infinite-length boxes, is re-examined in terms of the qualitative behavior implied. As the equations and the plots of the solutions show, there is a major difference between the behavior of the finite system (with discrete spec-trum) and that obtaining in the large-system limit. In the first case, a pulse-shaped wave "travels down the line" and comes back (and is sent off again) many times, completely "losing its shape" in the process (and subsequently re-gaining it on a much longer time scale infinitely often, due to the presence of a Poincare recurrence). In the large-system limit, on the other hand, a delta-impulse-like wave travels down the line only once (in finite time), and there is also no loss of shape upon its return after infinite time. Thus, there is no longer any even temporary "smearing out" of the initially sharply localized energy, and hence no "mixing" in the intuitive sense of the word. Nonetheless a dense spectrum is found (similarly as in the distribution theoretical case of an isolated delta-impulse in an infinite domain), and hence weak mixing in the sense of Lebowitz. The contradiction can be resolved at the expense of having to abandon some symmetry: by assuming the atom adjacent to two cavities of incommensurate lengths. Then the infinite system limit is unchanged (no return in finite time), but the transition is characterized by intuitive mixing of increasing effectiveness.

One-dimensional reaction-diffusion equations associated with the trimolecular model of Prigogine and Lefever ("Brusselator") are analyzed. A physical description of possibilities of keeping con-centrations of initial components constant is discussed. It is shown that the problem considering diffusion of initial components gives rise to an imperfect bifurcation problem. The diffusion equa-tions have been solved numerically by a continuation procedure for the fixed and zero flux boundary conditions. The analysis indicates that the models including diffusion of all reacting components do not admit an occurence of trivial solutions. These models, as a result, also exclude the pos-sibility of primary bifurcations. The models which consider diffusion of the initial components suppress the number of possible solutions of governing equations. These models may also predict both symmetric and asymmetric states. Apparently this type of models is more suitable for predic-tion of patterns of spatial organization in growth. Since the number of possible profiles is strongly reduced this principle may lead to a more deterministic way of an evolution process. Symmetric profiles occuring on an isola cannot be reached by an evolution process unless a large perturbation is imposed on the system.

The MINDO/3- and the MNDO-method have been used to determine the site of protonation of Aniline in the gas phase. We used the results of our semiempirical calculations together with the electrostatic "Solvaton-Model" to study the influence of the solvent on the energetics of the protonation of some amines and the site of protonation in Aniline. Our results indicate that the "Solvaton-Model", although neglecting specific interactions between solvent and solute such as the formation of hydrogen bonds, describes the change of the energy of solvation during the protonation in a rather successful agreement with experimentel results.

Molecular correlation functions have been determined for the infrared active vibrations ν 16 , ν 29 , ν 30 and ν 31 of neat liquid cyclohexane at different temperatures. The results have been com-pared with calculated reorientational correlation functions.

The photochemical cleavage of the endoperoxides of anthradichromene and benzodixanthene into the parent hydrocarbon and oxygen is shown to be an adiabatic photoreaction originating from an upper excited singlet state. This photochemical behaviour is described by a theory for the photochemistry of endoperoxides developed by Kearns and Khan.

In memory of W. H. We discuss the features of a microwave Fourier transform spectrometer in the X-and Ku-band as applied to the investigation of the hyperfine structure of rotational transitions. The Nitrogen-hyperfine structure of vinylisocyanide was measured and analysed.

The effect of an interdonor energy transfer is investigated on the following donor-acceptor systems in thin rigid cellulose acetate films: anthracene and tetracene (I), 9-methylanthracene and 2-aminobenzophenone (II), 9,10-diphenylanthracene and 2-aminobenzophenone (III). The donor quantum yield and fluorescence anisotropy in systems I-III are in good agreement with theoretical predictions for a model of a multi-step excitation energy transfer process. In mixed two-component solutions the donor fluorescence anisotropy is higher than in single-component solutions, indicating an interdonor excitation transfer preceding the donor-acceptor transfer in these binary systems.

A number of mathematical relations for the sextet polynomial are derived. A graph has been introduced (the so called C-graph), representing those properties of a benzenoid system which are essential in the sextet theory of Clar. The main structural properties of the C-graph are deter-mined. The obtained results contribute towards a better understanding of the algebraic and combinatorial background of Clar's theory of the aromatic sextet.

The photoluminescence decay time τ of neutral solutions of rhodamine B in ethanol was mea-sured for concentrations c from 10 -5 mol 1 -1 to 10 -2 mol 1 -1 at 295 K. The τ(C) curve observed is atypical, showing two regions of decreasing r. The drop over the range 4 X 10 -4 to 10 -3 mol 1 -1 was explained by the presence of two ionic forms of rhodamine B, and that at concentrations greater than 4 X 10 -3 mol 1 -1 - by rhodamine B dimers.

A combined pulse radiolysis-computer simulation method was applied for the elucidation of the complicated multiple H-attack on acridine orange in aqueous solutions at pH = 1 to 3. The simultaneous formation of three intermediates was established: semiquinone (H-addition on the N-atom of the chromophore group), R--species (reaction on the meso-C-atom) and H-adducts on the aromatic ring carbon. Their superimposed spectra were resolved, the individual extinction coefficients and the rate constants for their formation and decay were determined. The results are of importance in particular for understanding the decomposition of acridine orange applied as sensitizer in various devices for solar energy utilization.

The electron drift velocity in solid neon is reported for the field strength range 1 to 50 kV cm -1 .

Highly resolved vibronic absorption and fluorescence spectra of dioxido-p-terphenyl and the fluorescence spec-trum of trioxido-p-quaterphenyl in n-hexane at 77 K were obtained. The analysis of the vibrational structure in the excited singlet Si and in the ground So state gives funda-mental frequencies in the ground state in good agreement with those from infrared (IR) and Raman spectra.