Volume 23, Issue 7

We discuss and compare the theories of HAUSER and FESHBACH and P. A. MOLDAUER by a simple two channel model. It is found that after a good fit of parameters only the cross sections of compound-elastic scattering differ substantially. Most differences appear if there are a few open channels. The consequences for the cross section of compound nucleus formation and also for calculations by the evaporation mdel are considered. By our model an evident foundation is given for the statement that MOLDAUER'S theorie would be valid for 〈Γ λc 〉/D ≦ 1.

The internal conversion electron spectrum of transitions in the decay of (139 min) 165 Dy to 165 Ho has been studied using a high resolution iron-free double focusing β-ray spectrometer. In addition to γ rays previously reported eight new γ rays, mostly in the low energy region, have been observed. A decay scheme involving 17 excited levels is proposed for 165 Ho. Multipolarity data, obtained from the measurements of absolute or ratios of conversion coefficients of γ rays, were utilized for assigning possible spins and parities to the levels of 165 Ho. The experimental level structure is discussed in the light of nuclear models.

A formula is given for the correlation function of the bremsstrahlung emitted by a plasma, in terms of the correlations of the plasma density fluctuation. For the special case of stable and homogeneous plasmas in a steady state, the second-order correlation function is calculated as a functional of the particle distribution functions, and, as in the case of scattered laser light, found to have properties characteristic of a "chaotic” source. Generally, the possibility of gaining information about density correlations by photon counting experiments with bremsstrahlung turns out to be limited by the superposition of effects of many different Fourier components of the density fluctuations in the correlation functions of the radiation field.

Measurements of the photoemission caused by collisions of ground level He + - and Ne + -ions with Ar- and Kr-atoms have shown several multipletts of Ar II and Kr II within the investigated wavelength range of 3500 to 5500 A. At a high rate the charge transfer processes occur into excited states of Ar* and Kr*. The reactions are endothermic with a deficit of internal energy between 6 and 19 eV. The cross sections measured for several chosen transitions start at characteristic threshold energies between 10 and 25 eV. Above the threshold the cross sections rise slowly with increasing energy when Ne* is the colliding ion and very fast for He + . Above 50 to 100 eV the cross sections show nearly constant values. — The minimum kinetic energy values are calculated, which can just fill up the deficits of internal energy, and are shown to be equal to the measured threshold energies. Thus it follows that the pseudo-crossing of the potential energy curves of the quasimolecules occurs at an energy value equal to the asymptotic level of the above curve.

The heats of adsorption on weakly activated γ-aluminium oxide for a number of linear alkanes (from n-butane to n-nonane) and for 2.2.4-trimethylpentane have been determined by GSC and extrapolated to zero surface coverage. The dependance of the adsorption energy on the number of carbon atoms is discussed on the basis of the bidimensional gas model: it is shown that the interactions of the adsorbates with the oxidic surface are mainly due to London dispersion forces.

Nach Messungen anderer Autoren ergibt sich für den Diffusionskoeffizienten eines Edelgases in einem Alkalifluorid oberhalb 350 °C im Arrhenius-Diagramm ein geradliniger Verlauf mit einheitlicher Aktivierungsenthalpie. Dagegen zeigen Nichtfluoride einen Hoch- und einen Niedertemperaturbereich mit jeweils geradlinigem Verlauf und höherer Enthalpie in letzterem Bereich. — Zur Deutung dieses Verhaltens wird die Verteilung von Edelgasteilchen im thermodynamischen Gleichgewicht auf Anion-, Kation- und Zwischengitterplätze in einem solchen Kristall mit Schottky-Fehlordnung untersucht. Ferner wird Assoziation der Teilchen betrachtet. Aus der empirischen Verschiebung der genannten Bereiche kann bei Einzeleinbau auf eine Besetzung von Anion-Plätzen im Niedertemperaturbereich geschlossen werden, wobei aber nur die Annahme negativer Dotierung Entropiewerte richtiger Größenordnung ergibt. Bei Assoziation ergeben sich jedoch auch für die vermutete positive Dotierung die richtige Verschiebung und Entropiewerte richtiger Größenordnung, wenn die Teilchen im Niedertemperaturbereich auf Kationplätzen assoziiert sind. Bei den Fluoriden könnte der Einbau auf Anion-Kation-Divakanzen überwiegen. — Wenn die Strahlenschäden nicht ganz ausheilen, also der Kristall insofern nicht im thermodynamischen Gleichgewicht ist, kann die erwähnte Verschiebung auch auf einer Zunahme dieser Schäden beruhen.

The structures of liquid Hg and the dilute liquid Hg alloys with 0.5 and 2 atomic percent Cd, and 0.5 and 1 atomic percent Pb have been studied by x-ray diffraction using a theta-theta diffractometer with monochromator in the diffracted beam. The addition of 0.5 or 2 atomic percent Cd into Hg did not produce any detectable change in the interference function I (K), where K=4π (sin Θ)/λ, whereas small additions of Pb seem to reduce the asymmetry of the first peak of 1(K) which is observed in pure Hg. Small additions of Pb also cause a slight shift of the second peak of l (K) to smaller K-values. The present results have been used to offer a possible interpretation of the structure of Hg as observed in the liquid state.

It is shown by an etching method joined with microscopical observations that the structure of Rochelle salt crystals is not very much disturbed by dislocations and sudares. The correlation between the distributions of dislocations and sudares is obviously determined by the process of crystal growth. Measurements of the upper Curie-point and the dielectric constant are made in order to reveal some influence of these crystal defects on the dielectric properties.

In der vorliegenden Arbeit wird über die Berechnung der komplexen Streufaktoren für schnelle Elektronen an sechs Atomen unter Verwendung von Hartree-Fock-Potentialen bei fünf verschiedenen Beschleunigungsspannungen nach der Partialwellenmethode berichtet. Zur Berechnung der Werte wurde ein Näherungsverfahren verwendet, das sich aus der WBK-Methode ableiten läßt. Konvergenzkorrekturen für die Reihensummierung des Real- und Imaginärteils der komplexen Streufaktoren sind angegeben. Die Einflüsse des Näherungsverfahrens, der Anzahl der zur Summierung verwendeten Partialwellenphasen, sowie der Konvergenzkorrekturen werden diskutiert. Um die in Tabellenform vorliegenden Werte der komplexen Streufaktoren zur Auswertung von Elektronenbeugungsaufnahmen von Molekülen im Gaszustand besser verwenden zu können, wurden Beträge und Phasen der Streufaktoren durch analytische Ausdrücke angepaßt und die zur Approximation notwendigen Koeffizienten angegeben.

In extension of a previous paper partial ƒ-sum rules are derived for the rotator strengths of a freely rotating asymmetric top molecule whose permanent dipole moment interacts with the radiation field. In either of the two relations given the sums run over only part of the possible rotational transitions which start from any particular level: (1) J → J, J+1; (2) J → J, J-1. The two relations express stronger sum rules than the one reported formerly which may be shown to be dependent on those of the present paper. A short outline is given on how the “rotator strength” of this paper may be connected with the “oscillator strength for a rotational transition” of dispersion theory.

Some rules for mean amplitudes of vibration u are given. It is shown that the u values for bonded atoms can be calculated by a simple formula needing only stretching force constants and atomic masses. The values obtained for a number of XY 3 (C 3v ) and XY 4 (Td) molecules show generally less than 5% difference from the rigorously calculated ones. The data published in the literature are often several times too large. For the XY 3 (C 3v ) molecules a normal coordinate analysis in a M.V.F.F. approximation is given. From a new simple L matrix approximation method mean amplitudes of vibration have been calculated for these species which also agree very well with rigorously calculated ones.

Various approximate solutions to the second order secular equation ((G·F)L = LΛ) in molecular spectroscopy are considered. New relations between them are developed and their validities tested empirically. It is found that the methods are decreasingly valid in the following order: a. „Verfahren der nächsten Lösung“ which considers the point on the surface of all real allowed solutions of F nearest to that corresponding to completely uncoupled oscillators. b. A distribution of the potential energy in v 1 of V 22 = — V 12 or V 11 = 100%. c. F 22 a minimum, equivalent to L 12 =0, V 12 = —2 V 22 in v 1 and in v 2 V 22 =100%. This is the easiest solution to calculate (L matrix approximation method). d. The “Modified Valence Force Field” where F 12 =0. e. L matrix of maximum trace, equivalent to L = G 1/2 , having L 12 =L 21 . f. F 11 a maximum, equivalent to L 21 =0; V 12 = —2 V 11 in v 2 and in v 1 ,V 11 =100%, being the second root of a quartic equation in F 22 of which solution (b) is the first.

Im Frequenzbereich 12—19 GHz wurden bei Temperaturen um 650 °C Rotationsübergänge von 27 isotopen Molekeln des SnTe gemessen. Es werden Rotationskonstanten, Kernabstände, Koeffizienten der Potentialfunktionen nach DUNHAM und MORSE sowie Massenverhältnisse von Zinn- und Tellurisotopen mitgeteilt. Als Mittelwert für den Gleichgewichtsabstand der Kerne ergibt sich r e = (2,522 804 ± 0,000 029) Å.

The microwave spectrum of CF 3 CCl 3 has been investigated in the region from 15 to 40 GHz. A least squares analysis of the rotational constants gave the following structural parameters: d C–C = (1,5394 ± 0,001) A, d C–F = (1,330 ±0,001) A, d C-Cl = (1,7710 ± 0,0009) A, ∢ C—C—F = (109,55 ± 0,25) °, ∢ C—C—Cl= (109,55 ± 0,25) °. The splitting of the torsional satellite may be explained by the theory of KOEHLER and DENNISON.

Based on infrared intensity measurements of CH- resp. CD-stretching vibrations of the trigonal planar hydrocarbons azulene, 1,3-d 2 -azulene and cyclooctatetraene it was tried to find a relation between the CH-bond moments and the CCC-bond angles. Benzene and other polycyclic hydrocarbons with a CCC-bond angle of 120° have a CH-intensity of 0.099 cm 3 /mol per CH-bond. The CCC-bond angles in azulene lie between 104° and 133°. The total intensity of the CH-stretching vibrations in azulene is 0.814 cm 3 /mol, the CH-bond intensity for a CCC-bond angle of 104° is 0.058 5 cm 3 /mol. Furthermore the CH-bond intensity of cyclooctatetraene was measured to 0.161 cm 3 /mol. By comparing these values with a VB calculation — the change of the CCC-bond angle was expressed by different s- and p-portions on the CH-bond function — it was possible to prove a function representing the CH-bond moment as dependant of the CCC-bond angle. The polarity of the CH-bond moment has to be C + -H - between CCC-bond angles of ca. 110° and ca. 143°, and C--H+ below ca. 110° and above ca. 143°.

Farbzentren mit Absorptionen im Bereich des sichtbaren Lichtes entstehen bei Röntgen-Bestrahlung in Calcitkristallen, wenn die Kristalle durch Verformung eine hohe Störstellenkonzentration erhalten haben. Die Absorptionsspektren solcher Farbzentren werden ausgemessen und mit röntgenographisch bestimmten Störungsgraden verglichen. Die Bildung und die thermische Ausheilung der für die Entstehung von Farbzentren erforderlichen Störstellen wird quantitativ untersucht. Dabei wird festgestellt, daß mindestens zwei verschiedene Farbzentren auftreten, deren Konzentrationsverhältnis von der Temperaturvorbehandlung der gestörten Calcitproben abhängt.

Special effects of gasadsorption on epitaxy were discussed in previous papers 1 . In the present publication the influence of the adsorbed vapours on the epitaxial growth of fcc-metals on alkalihalides has been investigated in more detail. The results of the experiments demonstrate that the orientations of metal films are strongly influenced by the physical properties of the vapours the substrats are cleaved in. The thickness of the adsorbed layer is controlled by the dipole moment and the partial pressure of the vapours and additionnally by the substrat temperature and the deposition rate of the evaporated metal. Since the orientation of the metal films depends itself on the vapour covering of the cleavage planes, the orientation is also determined by these four quantities.

The influence of optically excited metastable triplet states on the spin lattice relaxation time T 1 of protons in anthracene is investigated at room temperature. From the H 0 -field dependence of T 1 in the presence of excited triplets we calculate the hopping time of triplet excitons τ c =(5±1) · 10 –12 sec. Especially in the low field region a new type of dynamic nuclear polarisation is observed. Triplet excitons, which are excited using unpolarized light produce via optical exciton spin polarisation an optical nuclear spin polarisation. Polarisation factors of more than 1000 are observed. Preliminary experiments with anthracene-tetracene mixed crystals are able to separate relaxation and polarisation effects due to mobile excitons from effects, which don’t need the mobility of excitons.

Zur Analyse der Torsionsfeinstruktur von Rotationslinien in schwingungsangeregten Zuständen wird ein Molekülmodell diskutiert, das drei Rotations-, einen Torsions- und einen Schwingungsfreiheitsgrad besitzt. Die theoretische Formulierung ist eine Verallgemeinerung der bekannten Principal Axis Method für Molekülmodelle ohne Schwingungsfreiheitsgrad. Bei bekannter Schwingungsfrequenz tritt nur ein weiterer Potentialparameter auf.