Showing papers in "Zeitschrift für Naturforschung A in 1968"
TL;DR: In this paper, it has been shown that the non-radiative mode excited by light can also radiate under certain conditions if they are excited by electrons (grazing incidence of electrons on a rough surface or at normal incidence on a grating).
Abstract: There are two modes of surface plasma waves: 1) Non-radiative modes with phase velocities Cü/k smaller than the velocity of light c. They cannot decay into photons in general. 2) Radiative modes with (o/k > c which couple directly with photons 1. The following paper is concerned with the excitation of these modes by light and their decay into photons. It has been shown that the radiative mode on thin silverand potassium-films can be excited by light and that the mode reradiates light almost into all directions with an intensity maximum at the plasma frequency cOp 2. It had been further observed that the non-radiative modes radiate under certain conditions if they are excited by electrons (grazing incidence of electrons on . a rough surface3 or at normal incidence on a grating 4) . The mechanism of this emission is in these cases always the same: The \"wave vector\" of the roughness of the surface or its irregularity changes the plasmon wave vector k so that a) in the case of the radiative mode light emission is found in directions in addition to that of reflexion and transmission, b) in the case of the non-radiative mode its wave vector is reduced so that the condition /c0, the wave vector of the inhomogeneous wave is (co/c) • Vsq' sin 0O (fq = 2.16 for quartz) and thus can excite a non radiative mode on the boundary of the prism for j/fq sin 0O > 1 or 90° > @o > 43°. If one vaporises a silver film directly on the quartz surface the inhomogeneous light wave penetrates into the silver film and excites a nonradiative mode on the boundary silver/air. The excitation will be highest for those frequencies which fulfill the dispersion relation of these surface plasmons.
2,790 citations
TL;DR: In this paper, the phase shift method was used to measure the radiative lifetimes of electronically excited states of N2O+, NO, O2+, CO+, and CO+ by means of a modulated electron beam.
Abstract: Radiative lifetimes of electronically excited states of N2O+, NO, O2+, CO+, and CO are measured by means of the phase-shift method. Excitation is performed by a modulated electron beam. Phase references are derived from He I, N2+, and CO+ transitions as well as from another independent method based on the very short decay time of the air fluorescence. Measurements are performed on the transitions N2O+ (B2 ∑u+ ➝ X2 IIg), NO (A2 ∑+ ➝ Χ2 II), O2+ (b4 Σg- ➝ a4 IIu), O2+ (A2 IIu ➝ X2 IIg), CO+(B2 ∑ ➝ X2 ∑), CO+ (B2 ∑ ➝ A2 II) , CO+ (A2 II ➝ X2 ∑), CO (b3 ∑+ ➝ a3 II), CO (B1∑+ ➝ A1 II). As far as feasable lifetimes of individual vibrational levels are measured. From the pressure dependence of the decay rates cross-sections for the quenching of the excited states by the parent molecules are obtained.
94 citations
TL;DR: The relation of selective miscibility between the liquid crystalline modifications has been explored by the investigation of binary diagrams of state in this article, where the authors show that the two highest members of the 4′-n-alkoxy-3′-nitrodiphenyl-4-carboxylic acids have a new smectic modification with the symbol D.
Abstract: Some members of the homologous series of the 4′-n-alkoxy-3′-nitrodiphenyl-4-carboxylic acids, which have been already described by Gray, were prepared. Their polymorphism in the smectic state was investigated. The relations of selective miscibility between the liquid crystalline modifications have been explored by the investigation of binary diagrams of state. By the use of the rule of selective miscibility, we can state: In this homologous series nematic and smectic A- and C-modifications occur. The two highest members of the series have a new smectic modification marked with the symbol D.
82 citations
TL;DR: In this paper, the behaviour of electromagnetic fields in electrically conducting media carrying out turbulent motions is investigated. But the authors focus on the mean fields defined by statistical averaging and not on the normal mean fields.
Abstract: This paper deals with the behaviour of electromagnetic fields in electrically conducting media carrying out turbulent motions. The basis is formed by Maxwell’s and the corresponding constitutive equations inclusive Ohm’s law, all with the neglections usual in magnetohydrodynamics. Attention is directed to certain mean fields defined by statistical averaging. From the equations mentioned above, except Ohm’s law, one gets equations of the same kind for the mean fields. In Ohm’s law, however, the transition to the mean fields leads to an additional term , the averaged vector product of the fluctuations in the velocity of the medium and the magnetic flux density. The investigation of this term makes up the centre in the elaboration of an electrodynamics of mean fields. As a very simple example a homogeneous isotropic turbulence showing reflexion symmetry is considered. In this case makes allowance for the introduction of a modified electrical conductivity. If the reflexion symmetry is violated, describes an effect allowing a dynamo action. Furthermore, a general method for calculation of for arbitrary turbulent motions is developed, and a survey is given of the results which can be expected for some special kinds of turbulence.
71 citations
TL;DR: In this article, a systematisch untersucht bzw. gemessen worden 1. Unterhalb von 2000 Å liegen von N2H4 Absorptionskoeffizienten nur für einige Wellenlängen vor 2.
Abstract: Von Wasserstoffperoxid und Hydrazin sind das Absorptionsspektrum und der Absorptionskoeffizient nur im Wellenlängengebiet oberhalb von 2000 A systematisch untersucht bzw. gemessen worden 1. Unterhalb von 2000 Å liegen von N2H4 Absorptionskoeffizienten nur für einige Wellenlängen vor2. Im Zusammenhang mit neueren photochemischen Arbeiten an H2O2 und N2H4 im Vakuum-UV2, 3 wurde deshalb der Absorptionskoeffizient dieser Moleküle im Bereich von 2000 bis 1200 Å untersucht.
54 citations
TL;DR: In this article, the authors developed the foundations for an electrodynamics of mean fields in turbulently moving electrically conducting media, where the turbulence is supposed to deviate from a homogeneous isotropic one showing reflexion symmetry, only due to a gradient of intensity.
Abstract: In a foregoing paper the foundations for an electrodynamics of mean fields in turbulently moving electrically conducting media were developed. With the method demonstrated there a special case is treated. The turbulence is supposed to deviate from a homogeneous isotropic one showing reflexion symmetry, only due to a gradient of intensity, i. e. of the mean square velocity. The calculations are carried out for small intensities. As a result, expressions for the modified conductivity introduced for homogeneous turbulence in the foregoing paper are given and discussed. The effect of the intensity gradient is illustrated by a simple example. Furthermore, a possibility is shown for describing the general result in terms of modified conductivity and permeability.
54 citations
TL;DR: In this article, the inner ionization potentials of indene, naphthalene, azulene, biphenyl, quinoline and isoquinoline were measured by an electron impact method.
Abstract: Photoelectron spectra of indene, naphthalene, azulene, biphenyl, quinoline and isoquinoline are reported, and some inner ionization potentials of naphthalene, azulene, biphenyl and biphenylene measured by an electron impact method are also given. A close correlation is found between the inner ionization potentials of the hydrocarbons and π-electron orbital energies given by the zerooverlap Hückel approximation.
53 citations
TL;DR: In this paper, the incorporation of titanium in sapphire may prevent a development of the damaging electron avalanche in the following way: Ti probably replaces Al forming an acceptor state.
Abstract: für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution 4.0 International License. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namensnennung 4.0 Lizenz. The mechanism of destruction may be as follows. Electrons are lifted from the valence band into the conduction band by multiphoton processes. These conduction electrons are rapidly gaining enough energy in the intense laser beam to create further conduction electrons resulting finally in an electron avalanche which produces the damage. The existence of such a hot electron gas should manifest itself above the damage threshold by the emission of a broadband continuum which we have, in fact, observed between 400 and 800 m/u 5. The incorporation of titanium in sapphire may prevent a development of the damaging electron avalanche in the following way: Ti probably replaces Al forming an acceptor state. Judging from the titanium induced strong UV-absorption at long wavelengths, the energy of this acceptor state appears to be situated several eV
46 citations
TL;DR: In this paper, two constants Xa and ϑ0 are determined, for each element and electron energy, from the measurements of xk at four different objective apertures.
Abstract: Electron transmission experiments under electron microscope conditions were done with C-, Ge- and Pt-films to get information about the influence of electron energy and objective aperture. One gets an exponential law of transmission for small mass thicknesses x of the objects and can calculate the “contrast thickness” xk (in T = exp(— x/xk)). Using the Lenz theory, two constants Xa and ϑ0 are determined, for each element and electron energy, from the measurements of xk at four different objective apertures. xa is related to the total elastic scattering cross section and ϑ0 is the half width of the atomic scattering amplitude ƒ(ϑ). The variation of xa and ϑ0 with electron energy is not in agreement with the theory using the first Born approximation and a simple screened atomic potential. But using these two experimentally determined constants in a plural scattering theory of LENZ, good agreement between calculated and experimental deviations from the exponential law of transmission up to mass thicknesses of 300 µg · cm-2 is obtained. To get better theoretical values of xk, the complex atomic scattering amplitudes were calculated quantum theoretically with the WKB-method and Hartree potentials. The values agree with the experimental results for Ge- and Pt-films. For carbon there is a large contribution by inelastic scattering making a direct comparison with experimental results difficult. The energy dependence of xa shows saturation for high voltages, as expected by theory. At high voltages the difference in the xk-values for films with different atomic numbers is larger, resulting in lower xk-values for platinum. But at very low voltages the xk-values of carbon are lower than those of platinum. Some measurements of xk at 60 keV on targets of noble gases confirm the absence of a large difference in contrast between atoms in the gaseous and condensed amorphous state.
44 citations
TL;DR: In this article, it was shown that spinlattice relaxation is effective at rather low temperatures and can no longer be interpreted in terms of classical hindered rotations of the methyl groups.
Abstract: The proton magnetic resonance and relaxation of o-, m- and p-xylene has been studied at various temperatures between the melting point and 2°K. Motionally narrowed second moments of the proton lines of about 10 G2 have been observed over the whole temperature range. Spinlattice relaxation is effective at rather low temperatures and can no longer be interpreted in terms of classical hindered rotations of the methyl groups. Quantum mechanical tunneling through the barriers hindering the reorientations is considered instead. Furthermore it is proposed to explain the observed decay of relaxation rates at low temperatures as a consequence of some kind of bottleneck in the energy transfer between torsional motions and other degrees of freedom in the solid. On the basis of a simplified model a quantitative explanation of the experimental data has been possible using elements of the theoretical treatment of Stejskal and Gutowsky. The potential barriers are of sixfold and of threefold symmetry. From the experimental data absolute barrier heights of 2,2 (o-xylene), 0,27 (m-xylene) and 1,1 kcal/Mole (p-xylene) could be calculated.
42 citations
TL;DR: In this paper, a plane crystal spectrometer was used to measure relative integrated intensities of Kα X-ray satellites in fluorescence spectra of Na in NaF, and of Mg, Al, Si in metals and oxides.
Abstract: A plane crystal spectrometer was used to measure relative integrated intensities of Kα X-ray satellites in fluorescence spectra of Na in NaF, and of Mg, Al, Si in metals and oxides. A comparison between the measured intensity of the Κα'α3α4 satellite group and the intensity obtained from electron excitation measurements indicates that the production probability of KL double-hole states is independent of the excitation mode. The measured intensities in metals are in agreement with calculated intensities based on the sudden approximation theory of x-ray satellites of free neon-like ions. The bond in fluoride and oxides was shown to increase the relative intensity by about 13%. From intensity considerations, the Κα5α6 satellite group was attributed to KL2 triplehole states.
TL;DR: In this paper, a crystal field formalism is developed, which allows a quantitative treatment of the spectra in correspondence with crystallographic data, and the calculated ligand-field parameters Δ do not differ much from those of Ni2+ and Co2+ in the same host lattices.
Abstract: The remission spectra of a number of Cu2+-containing oxidic solids in the region between 3500 and 25 000 cm-1 were found to show always — independent of the macroscopic lattice-symmetry — the typical three-band-structure expected for tetragonally distorted octahedra. It could be derived from the spectra of the perovskite-mixed-crystals Sr2(CuχZni _xMe)O6 [Me=W6+, Te6+] (0<χ≦1) hat these three bands have to be assigned to the transitions B1g → A1g , -→ B2g and → Eg with increasing energy. A crystal field formalism is developed, which allows a quantitative treatment of the spectra in correspondence with crystallographic data. The calculated ligand-field-parameters Δ do not differ much from those of Ni2+ and Co2+ in the same host lattices.
TL;DR: Schwanz-banden des CO+ müssen 3 bis 4 eV von der kinetischen Energie des Ne+ in innere Energi übertragen werden.
Abstract: Teil im A2Z7u-Zustand gebildet werden. Beim C02 tritt neben der Strahlung, die vom C02+ herrührt, ein ebenso hoher Anteil von CO+ auf. Das Ion CO+ entsteht durch dissoziativen Ladungsaustausch aus C02 . Trotz der Anregungen bleiben sämtliche Reaktionen mit der Ausnahme des dissoziativen Prozesses um 3 bis 5 eV exotherm. Zur Anregung der beobachteten KometenSchwanz-Banden des CO+ müssen 3 bis 4 eV von der kinetischen Energie des Ne+ in innere Energie übertragen werden. Eine ausführliche Darstellung dieser Untersuchungen befindet sich in Vorbereitung.
TL;DR: In this article, a plane source method for non-steady state measurements of the thermal conductivity and thermal diffusivity of transparent liquids is applied to the study of molten salts.
Abstract: A recently developed plane source method for non-steady-state measurements of the thermal conductivity and thermal diffusivity of transparent liquids is now being applied to the study of molten salts. In these first measurements sodium nitrate and potassium nitrate have been investigated from their melting points to about 450°C. No temperature dependence of the thermal diffusivity can be established for either of the liquids, whereas the thermal conductivity in both cases increases very slowly with the temperature. A description of the experimental arrangement is included.
TL;DR: In this paper, the absorption oscillator strengths of 44 S I- and 9 S II-lines between 1100 and 2000 Å were measured in emission, where the light source is a wall-stabilized arc burning in definite argon-SF6 mixtures.
Abstract: The absorption oscillator strengths of 44 S I- and 9 S II-lines between 1100 and 2000 Å are measured in emission. The light source is a wall-stabilized arc burning in definite argon-SF6 mixtures. Normal-intensities are produced by the same source. The evaluation of particle densities is carried out without assuming constancy of mixture ratio and knowledge of any transition probability.
TL;DR: In this paper, the electron drift velocity in argon, helium, nitrogen, and hydrogen was determined as a function of E/p [V/Torr cm] at room temperature and for high pressure up to 42 at.
Abstract: By means of a time of flight method the electron drift velocity ν _ in argon, helium, nitrogen, and hydrogen was determined as function of E/p [V/Torr cm] at room temperature and for high pressure up to 42 at, at which no measurements were as yet available. In He and H2 E/p was decreased to that range where the electrons are in thermal equilibrium with thet gas. In N2 measurements were extended nearly to this range, and in Ar measurements were carried out for E/p well above this range of thermal equilibrium. The accuracy from 1% to 1.5% in the available pressure range enabled an examination of the similarity rule. For the diatomic gases N2 and H2 the measurements show that for constant E/p, in the range E/p < 1, the drift velocities decrease with increasing pressure. This effect was not found in Ar. In He no effect was found in the pressure range up to 8400 Torr (or it lies within the limits of error).
TL;DR: In this paper, it was shown that the delayed fluorescence is at least mostly due to a thermally activated triplet triplet annihilation in Naphthalene-h8.
Abstract: Measurements of the phosphorescence and delayed fluorescence emission at temperatures between 1.6 and 50 °K are reported for the following mixed crystal systems: Naphthalene-h8 in Naphthalene-d8 and Durene; Thionaphthene, Durene and β-Methyl-Naphthalene in Naphthalene-h8 . The emitting species is either the guest molecule (trap emission) or the vicinity of the guest molecule (disturbed exciton emission of the host) . By an analysis of the temperature dependence of the intensities of delayed fluorescence and phosphorescence it can be shown that the delayed fluorescence is at least mostly due to a thermally activated triplet triplet annihilation. Triplet energy is transferred from a trap to the annihilation partner by using the exciton band of the host. Spectroscopic and thermal energy gaps between trap levels and the host exciton band are measured. In addition we report some lifetime measurements in these crystals.
TL;DR: In this article, a modified version of the method of Kivelson and Wilson for calculating centrifugal distortion constants (tαβγδ) in terms of matrix notation is presented.
Abstract: The method of Kivelson and Wilson for calculating centrifugal distortion constants (tαβγδ) is treated in terms of matrix notation. A modified method is developed, by which the quantities of tαβγδ are obtained with the aid of certain elements Tαβs(t), rather than the partial derivatives of inertia tensor components, Jαβs(t), used in the method of Kivelson and Wilson. The Tαβs(t) elements may easily be evaluated for a given molecular model from the equilibrium position vectors and the Wilson s vectors. The bent symmetrical X Y2 molecule model is used for exemplification of the developed theory. Also included are some numerical results for a number of molecules of the bent symmetrical X Y2 type.
TL;DR: In this article, an electron diffraction investigation of unstable gaseous disulfane using the sector-microphotometer method has been carried out, and the results of these measurements and the available microwave data together yield the following molecular parameters for H2S2: d (S-H) = 1.352 ± 0.015 A, angle (HSS) = 91°57′, d(S-S) = 2.055± 0.001 A, dihedral angle = 90°37′ ± 3′.
Abstract: An electron diffraction investigation of unstable gaseous disulfane using the sector-microphotometer method has been carried out. The results of these measurements and the available microwave data together yield the following molecular parameters for H2S2: d (S—H) = 1.352 ± 0.015 A, angle (HSS) = 91°57′, d(S—S) = 2.055 ± 0.001 A, dihedral angle = 90°37′ ± 3′.
TL;DR: In this article, the Larmor-frequencies of these alkali nuclei relative to 2H have been measured with high accuracy and an extrapolatiton to vanishing concentration was made.
Abstract: The NMR signals of the nuclei 2H, 6Li, 7Li, 23Na, 87Rb and 133Cs have been investigated in aqueous solutions. The ratios of the Larmor-frequencies of these alkali nuclei relative to 2H have been measured with high accuracy. Because the Larmor-frequencies depend on the concentration of the aqueous solutions, an extrapolatiton to vanishing concentration was made. From these ratios of Larmor-frequencies, a magnetic moment for the alkali nuclei has been derived and has been compared with the available nuclear magnetic moments from atomic beam or optical pumping experiments. The difference in the magnetic moments results from the shielding of the alkali nuclei by the water molecules around the ions. The shielding constants are: σ (Rb+) = — (2.0 ± 0.2) ·10-4 and σ (Cs+) = — (3.4 ± 0.1) · 10-4 relative to the free ion. The shift of the 133Cs NMR line as a function of the concentration of aqueous solutions of Cssalts is given in detail. The influence of the chlorides of some elements in the iron group and of some lanthanide elements on the position of the 133Cs NMR line is shown.
TL;DR: In this paper, a theoretical analysis was carried out of the 4-spin spectrum of a rotating methyl group and one coupled proton in terms of the two direct and one scalar spin-spin couplings and the chemical shift difference between the two groups of protons.
Abstract: The proton magnetic resonance spectra of ethyne (acetylene, I), 3-chloro- and 3-bromo-propyne (II, III), 1,4-dichloro-2-butyne (IV), propyne (V), 1,3-pentadiyne (VI) and 2,4-hexadiyne (VII) were investigated in the nematic phase of 4,4-di-n-hexyloxy-azoxybenzene. A theoretical analysis was carried out of the 4-spin spectrum of a rotating methyl group and one coupled proton (e. g. compounds V and VI) in terms of the two direct and one scalar spin-spin couplings and the chemical shift difference between the two groups of protons. Correspondingly, the spectrum of two equivalent rotating methyl groups (e.g. compound VII) was calculated in terms of the two direct and one scalar spin couplings. The chemical shift differences of the signals of the acetylenic protons in the nematic and the isotropic phase indicated that compound I was preferentially oriented perpendicular to the magnetic field, whereas an increasing parallel orientation of the carbon triple bond with respect to the magnetic field was found for compounds II, III, V and VI. The chemical shift anisotropy of the acetylenic protons were between 8.1 × 10-6 and 13.1 × 10-6, whereas the values for the methyl protons were almost zero. The absolute signs of the scalar couplings J (H, CH3) of V and of J (CH3, CH3) of VII were found to be negative and positive, respectively, in accordance with theoretical predictions of Karplus. Values for the relative proton-proton distances were calculated for compounds V, VI and VII and were compared with microwave and electron diffraction data. The agreement was good with the microwave data for V. Discrepancies with the less accurate structural data available for VI and VII are tentatively explained by the assumption that in these diacetylenes the H—C—H-bond angles of the methylgroups are slightly increased (∼ 110°) compared to V (108°25′).
TL;DR: In this paper, an extension of the Onsager model to include local fluctuations of the electric field has been developed, based on previous theories, and an approximate expression for the mean square of the effective electric field was derived.
Abstract: The optical properties of molecules may he affected by an electric field. With suitable molecules, these effects allow to determine the electric dipole moments and certain components of the polarizability tensors in the ground state and in excited electronic states, the directions of transition moments and certain components of the transition polarizability tensors. The magnitude of the electrooptical effects depends on the effective electric field acting on the molecule. In preceding papers the representation of the effective field was based on the Onsager model. More recent experimental investigations have shown that this approximation is not sufficient when using polar solvents. Here, local fluctuations of the electric field have to be taken into account. Basing on previous theories, an extension including these effects is developed which agrees with the experimental results, as will be shown in the following paper7. Also, an approximate expression is derived for the mean square of the effective electric field
TL;DR: In this paper, various approximate solutions to the second order secular equation ((G·F)L = LΛ) in molecular spectroscopy are considered and new relations between them are developed and their validities tested empirically.
Abstract: 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 v1 of V22= — V12 or V11 = 100%. c. F22 a minimum, equivalent to L12=0, V12= —2 V22 in v1 and in v2 V22=100%. This is the easiest solution to calculate (L matrix approximation method). d. The “Modified Valence Force Field” where F12=0. e. L matrix of maximum trace, equivalent to L = G1/2, having L12=L21 . f. F11 a maximum, equivalent to L21=0; V12= —2 V11 in v2 and in v1,V11=100%, being the second root of a quartic equation in F22 of which solution (b) is the first.
TL;DR: In this paper, a semi-empirical LCAO-MO theory of WALSH was used to calculate the g-factor shift of the SO2-xSO2 ion.
Abstract: From the triatomic molecule SO2 with 18 valency electrons we generated the mononegative radical ion with the aid of electrolytic techniques. In this way we could vary the radical concentration over a wide range and could also study the influence of counter ions and solvent molecules. The semi-empirical LCAO-MO theory of WALSH was used to calculate the g-factor shift. UV spectroscopic data of SO2 and Hückel-MO-calculations of the spin density distribution of the unpaired electron in the antibonding MO of SO2- resulted in Δgtheor = (3.9 ± 0.6) x 10-3 which agrees rather well with Δgexp = (3.414 ± 0.003) x 10-3. The quoted error of the theoretical value refers to approximations, which have to be introduced in addition to the approximations of the LCAO-MO theory of WALSH. The HMO spin density distribution compares nicely with the distribution calculated from anisotropic hfs constants of SO2- in a KCl single crystal which have been measured recently by SCHNEIDER et al. Higher concentrations of SO2 molecules resulted in another EPR line with Δgexp = 4.6 x 10-3 which we attribute to the solvated radical ion (SO2)xSO2-. From the temperature dependance of the concentration ratio of the radical species in we determined W = - 6.9 kcal mol-1, x = 2, and K(0 °C) = 8.0 x 10-5 mol2 lit-2.
TL;DR: In this paper, a Bendix time of flight mass spectrometer has been modified to enable the determination of some ion-molecule reaction cross sections in the energy range 1 -100 eV.
Abstract: A Bendix time of flight mass spectrometer has been modified to enable the determination of some ion-molecule reaction cross sections in the energy range 1 — 100 eV. In the reactions studied X+ + D2 → XD++D where X may be Ar, N2 or CO, the results obtained agree with the predictions of the polarization theory in the range below 10 eV despite the fact that no intermediate complex is formed at these energies. Between about 10—50 eV where spectator stripping occurs the cross section follows an approximate E-l dependence. Above these energies the results are consistent with a transition to a region in which knock-on processes predominate and where an impulse approximation treatment would be valid.
TL;DR: In this article, the Mikrowellenspektrum des N-Methylpyrrols and des D3-N-methyltetroben was untersucht, um das niedrige Hinderungspotential der internen Rotation der Methylgruppe zu bestimmen.
Abstract: Das Mikrowellenspektrum des N-Methylpyrrols und des D3-N-Methylpyrrols wurde untersucht, um das niedrige Hinderungspotential der internen Rotation der Methylgruppe zu bestimmen. Mit dem Spektrum sind jeweils zwei unterschiedliche Sätze von Potentialparametern V6 und V12 verträglich. Ferner wurden das Dipolmoment und die Quadrupolkopplungskonstanten bestimmt.
TL;DR: In this paper, the influence of optically excited metastable triplet states on the spin lattice relaxation time T1 of protons in anthracene is investigated at room temperature.
Abstract: The influence of optically excited metastable triplet states on the spin lattice relaxation time T1 of protons in anthracene is investigated at room temperature. From the H0-field dependence of T1 in the presence of excited triplets we calculate the hopping time of triplet excitons τc=(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.
TL;DR: The absorption and ionization cross sections of molecular hydrogen for the wavelength region from 850 to 792 A are given in this paper, where it is shown that even above the ionization limit the absorption due to the D-state of the molecule leads to dissociation.
Abstract: The absorption and ionization cross sections of molecular hydrogen for the wavelength region from 850 to 792 A are given. This region contains the dissociation and ionization limit as well. The rotational structure of the bands could partially be resolved in this experiment. As the dissociation of the molecule results in an excited hydrogen atom, this process can be followed by measuring the atomic fluorescence. Part of the excited atoms is found to be in the metastable 2 2S-state. From fluorescence as well as absorption and ionization measurements it can be shown, that even above the ionization limit the absorption due to the D-state of the molecule leads to dissociation. The experimental results seem to point out, that the spectroscopic value of the ionization limit has to be shifted to lower energies.
TL;DR: In this article, the absolute transition probabilities of the KLL Auger transitions of neon have been calculated in units of 10-3 e2/ħ a0=4.
Abstract: From the Auger transitions KL2,3L2,3(1D2) of neon and L3M2,2M2,3 (1D2) of argon the level widths Γ(K) of neon and Γ (L3) and Γ (L2) of argon have been determined by folding Lorentzian distributions with the spectrometer function. The values found are: Γ(K) = (0.15 ± 0.03) eV, Γ (L3) = Γ (L2) = (0.16 ± 0.02) eV. From the level width Γ(Κ) of neon and the relative intensities of the KLL Auger lines of neon, determined very recently, absolute transition probabilities of the KLL Auger transitions of neon have been calculated to be (in units of 10-3 e2/ħ a0=4.1 · 1013 sec-1) : KL1L1(1S0) = 0.35 ± 0.07;KL1L2,3 (1P1) = 0.96 ± 0.19;KL1L2,3 (2P) = 0.35 ± 0.07; KL2,3L2,3,3 (1S0) = 0.55 ± 0.11;KL2,3L2,3 (1D2) = 3.28 ± 0.66;KL2,3L2,3 (3P0,2) = 0 . Whereas the experimental total transition probability KLL is in good agreement with theoretical values of the transition probability for Ζ=10, determined by extrapolation of Callan’s values for Ζ ≧ 12 and of Archard’s values for Z=11, 12, 15, 16, 17, 18, the experimental transition probabilities of the fine structure components do not agree with Callan’s values and agree only in some cases with Archard’s values.
TL;DR: In this article, the komplexen Streufaktoren für schnelle Elektronen an sechs Atomen unter Verwendung von Hartree-FockPotentialen bei fünf verschiedenen Beschleunigungsspannungen nach the Partialwellenmethode berichtet.
Abstract: 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.