Volume 35, Issue 5

The following rotational spectra of carbonyl sulfide have been accurately remeasured with a beam-absorption spectrometer: 16 O 12 C 32 S in the vibrational ground state and in the vibrational state 0 1 1 0. 16 O 12 C 34 S in the vibrational ground state. The ground state spectra of the following isotopic species have been measured with a video spectrometer: 17 O 12 C 32 S, 18 O 12 C 32 S, 16 O 13 C 32 S, 16 O 12 C 33 S, 16 O 12 C 36 S, and 16 O 13 C 34 S. Our measurements have enabled us to improve the molecular constants notably for these cases.

The ESR-behaviour of antiferromagnetic and almost stoechiometric CrN is thoroughly investigated above its Neél-point. For polycrystalline samples a spectroscopic splitting factor g =1.965 and a differential line width ⊿B = 56,7 mT is measured at room temperature. All resonance lines exhibit Lorentzian character to a high degree. In the temperature range between 300 K and 520 K the ESR-intensity can satisfactorily be described by a model of local ordering. Its binding energy is computed to be about ⊿E = 500 ± 20 cm -1 . A more refined analysis shows a systematic change of ⊿E with temperature and a discrepancy between the Neel-point T N and the temperature T s characterizing a singular behaviour of the line width ⊿B. Apart from these deviations originating in a magnetic ordering of the fourth kind, the cluster-model gives an isotropic exchange between next nearest neighbours of J 2 = -33.2 cm -1 . This result is confirmed by molecular field computations.

a-type rotational transitions of molecules in the vibrational ground state of thioketene, H 2 C=C=S, have been measured in the millimeter wavelength region. The measurements yielded improved rotational constants: A = 286 655(82) MHz, B = 5 659.47596(72) MHz, C = 5 544.51269(72) MHz. A detailed centrifugal distortion analysis by means of Watson's S-reduced Hamiltonian led to the determination of four quartic, two sextic and two higher order distortion constants: D J = 1.08569(4) kHz, H JK = 0.716(20) Hz, D JK = 168.269(77) kHz, H KJ = -408.7(73) Hz, D 1 = -25.46(68) Hz, L KJ = 0.65(24) Hz, d 2 = - 5.21(35) Hz, S KJ = -0.0533(24) Hz. Effective rotational and centrifugal distortion constants using planarity conditions were calculated. The electric dipole moment of thioketene was determined to be μ = 1.01(3) D.

The information about an observable A provided by an indirect experiment in which observable B is measured is used as a criterion for comparing the performance of different observables B and for selecting an optimal initial state.

A new transport property, the self-exchange velocity (SEV) of neighbouring unlike ions, has been evaluated from molecular dynamics simulations of molten LiCl, RbCl and LiRbCl 2 at 1100 K and the mixture at 750 K. From the increase of the SEV's in the order Rb + (pure salt) <Li + (mixture) < Rb + (mixture) < Li + (pure salt), it is conjectured that there is a strong correlation between the SEV’s and the internal mobilities. An interpretation of the Chemla effect in its dependence on temperature is given. The pair correlation functions and the self-diffusion coefficients are also calculated and discussed.

The formation reaction of Mg 2 Mo 3 O 11 from MgO (single crystal) and MoO 3 (pellet) has been investigated in the temperature range 873-973 K. Supported by an analysis of the transport properties a mechanism is proposed involving a unidirectional transport of Mo 6+ via V 6′ Mo and of oxygen via gas phase. The transport properties of MgMoO 4 (the other intermediate compound in the system MgO-MoO 3 ) were also studied and the results were found to agree with the mechanism observed in a previous work on the basis of kinetic and structural considerations.

An experimental method is described which allows the determination of the diffusion coefficient D of an aromatic hydrocarbon in its lowest and metastable triplet state T 1 with an absolute accuracy of ±5%. D was determined at 25 °C. With anthracene the temperature-dependence of D was measured from 0°C to 60°C in hexane and from 20°C to 89°C in hexadecane; it was found to be in good but not perfect agreement with the Stokes-Einstein equation. With the investigated systems, D of molecules in T 1 is estimated to be at most 10% smaller than D of molecules in the ground state. No evidence for the formation of triplet excimers was found. Some applications of the method are proposed, and in this connection some questions concerning the kinetics of diffusion-controlled reactions of molecules in T 1 and the existence of triplet excimers are discussed.

The first few bands in the photoelectron (Hel) spectra of ketenimines R 1 R 2 C-C=NR 3 (R 1 ,R 2 =H, CH 3 , C 5 H 6 , CH 2 =CH; R 3 =alkyl or aryl group) are assigned to the corresponding molecular orbitals. The assignment is based on SCF-MO calculations made at three different levels (CNDO/2, ab-initio STO-3C and 4-31G) coupled with perturbational molecular orbital analyses. The π-orbitals of the unsaturated substituents are found to interact with one of the two perpendicular π-electron systems of the〉C=C=N- residue, the critical factor being the position of attack of the substituent. The relevance of these results on the site selectivity observed in cycloaddition reactions of these species is discussed.

A system may be characterized by its dynamics as well as by its structure. Several kinds of schematic drawings have been proposed to represent the structure of a system. Here, the representation of the structure by free groups is discussed. Free groups are an abstract mathematical tool, which permits the systematic treatment of a structure. The suggestion is exemplified by its application to a chemical kinetic model. The structure of the model is given (coded) by a linear sequence of symbols. The interaction of the environment with the structure (mutation) and the relation between structure and systemic boundaries (finiteness) are treated. The concept probably also applies to biological systems. Also, context-free languages could be used as alternate representations of system structures.

Heterogeneous isotope exchange rates of Na + , Ca + , Ba 2+ and Sr 2+ in mono-and biionic resin exchangers (Merck I) have been measured under conditions where diffusion is rate determining. For the self-diffusion of Na + , Ba 2+ and Sr 2+ linear Dt/r 2 - f(t)-curves are obtained. Cs-isotope exchange shows non-ideal diffusion kinetics. In mixed Ba-exchangers the self-diffusion coefficients of Ba 2+ and Sr 2 depend on the ionic composition of the exchanger phase. Ion exchange rates have been measured for Ba/Sr 2+ -exchange and its reversal. Computed curves are presented using Helfferich’s theory of ion exchange and an extended treatment with activity correction terms and concentration dependent self-diffusion coefficients. Computed and experimental curves are discussed.

The infrared spectra of 1-cyano-3-butyne were recorded in the region 4000-50 cm -1 in the vapour and liquid states, as an amorphous and as two different crystalline solids at 90 K. In addition the compound was studied as a high pressure crystalline solid at ambient temperature. Raman spectra of the liquid, including polarization measurements, and of the amorphous and the two crystalline solids at 90 K, were obtained. The spectra revealed the existence of two conformers, anti (C s ) and gauche (C 1 symmetry) in the vapour, liquid and in the amorphous solid. When annealed to ca. 140 K a metastable crystal containing one conformer (probably the gauche) was formed, when annealed to ca. 190 K a stable crystal was obtained having the other conformer (probably the anti). The latter conformer was present in the high pressure crystal. Very accurate spectral data for each conformer were collected from the two crystalline solids, making complete assignments for the anti and gauche conformers feasible. The assignments were checked by a normal coordinate analysis. A simple diagonal force field was derived in which the same force constants were employed for the anti and gauche conformers. The mean amplitudes of vibration were calculated for both conformers.

The infrared absorption of the O-D stretching fundamental of HDO in concentrated aqueous (HDO/H 2 O) LiCl solutions to a maximum of 40 mole percent salt has been measured. Data for the wavenumber of maximum absorption, ν̄(max), and for the integrated molar absorptivity B up to pressures and temperatures of 2800 bar and 350 °C, respectively, are reported and discussed. Toward high salt concentrations, the dependence of ν̄(max) on temperature and on LiCl concentration decreases. The wavenumber data indicate a transition from "water-like" to "melt-like" behaviour at about 12 to 15 mole percent LiCl.

Patterns of spatial concentration profiles arising in one-dimensional reaction-diffusion systems in the course of variations of the characteristic dimension of the system (growth) are analyzed. The spatial profiles established and their changes depend on the character of the steady state pattern dependence on length. If the families of solutions (spatial profiles) arising at L = nL 1 *, nL 2 * form closed curves, and a slow (quasistationary) linear or exponential increase of the characteristic dimension is considered, then subsequently more complex patterns of spatial concentration profiles appear regularly in a reproducible way. The system keeps every established pattern for a fixed interval of time which depends on the rate of growth. Implications for two different interpretations of the morphogen gradient formation in the models of embryogenesis are discused.

We investigated the pressure dependence of the T 2 - relaxation time for several rotational transitions of acetal-dehyde, CH 3 CHO. No difference in the relaxation of A- and E-species transitions could be detected. The analysis was performed in the time and frequency domain.