摘要:

AbstractThe complex interplay of anisotropic rotational diffusion, ground‐state population recovery and intersystem‐crossing involved in a transient absorption experiment is treated theoretically via balance equations for the angular‐dependent population densities. An approach to the solution of this problem is presented that avoids the formalistic Green's function method and provides an analytical expression for the time course of the absorption relaxation in the small‐signal case with sin2‐pulse excitation and interrogation. The approach from first principles allows a straightforward discussion of the large‐signal case. It can be shown that a rotation‐free measurement is possible by the 54.7°‐method irrespective of the excitation intensity and anisotropy of the molecular rotator. — Experiments are performed with a cw pulse photometer which delivers precise absorption‐relaxation plots that are amenable to computer evalution by least‐square methods. Even though the dye molecules Rhodamine 6 G, Erythrosine B and Pyronine G, Acridine Orange are definitely oblate and prolate rotators, respectively, their rotational behaviour is dominated by a single‐exponential decay. From this it is concluded that rotational diffusion obeys the “stick” boundary condition and that the transition moment for the S0→ S1transition lies in the molecular plane pointing along the long axis. This agrees well with a simple free‐electron model of

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830302

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractDie Beobachtung der Obertonspektren der OH‐Streckschwingung von Alkoholen ‐ einschließlich solcher, die intramolekulare Wasserstoffbrücken bilden ‐ liefert weitere Informationen über die Moleküstruktur und trägt zur experimentellen Bestätigung bislang bekannter Vorstellungen über den Zusammenhang zwischen den Spektren von Molekülschwingungen und den zwischenmolekularen Wechselwirkungen sowie der Moleküldynamik in flüssiger Phase bei. Durch Verwendung von Kohlenwasserstoffen als Lösungsmittel wird die Streckschwingung der OH‐Gruppe in gauche‐Stellung als separate Bande beobachtet. Ein Vergleich mit dem Grundschwingungsspektrum zeigt, daß die Zeitauflösung des Beobachtungsmittels erst bei den Obertönen zur Abtrennung dieser Bande ausreicht. Daraus wird eine Lebensdauer dieser Struktur von mindestens 3 ps abgeschätzt. Aus der Zunahme und der Angleichung der Profilbreiten beim Übergang in den Obertonbereich wird gefolgert, daß eine inhomogene Störfeldverteilung (Phasenrelaxation im Zeitbild) der dominierende Verbreiterungsmechanismus in diesen Spektralbereichen ist. Das besondere Verhalten der durch Wasserstoffbrücken beeinflußten OH‐Schwingungen unterstreicht diese Vorstellung. Der hohe Gaußformanteil in den Profilen der zweiten Obertonspektren wird als Abnahme der durch die Moleküldynamik bewirkten

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830303

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractThe pressure and temperature dependencies of the fluorescence quantum yield of 9‐methylanthracene (MA) and 9,10‐dibromoanthracene (DBA) were investigated in heptane and toluene, respectively. The data were interpreted in terms of the Eyring transition state theory. ‐In the case of MA it was found that the activation enthalpy ΔH* of S1→ T2intersystem crossing increases with increasing pressure, while for DBA no pressure dependence of ΔH* was observed. An increase in the fluorescence quantum yield at higher pressures was found for both compounds and was attributed to a positive activation volume S1→ T2, which inhibits S1→ T2intersy

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830304

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractExperimental results have been obtained for the density ρ, electrical conductivity σ, and the thermoelectric powerSof liquid rubidium as a function of temperature (300–1700°C) and pressure (1–400 bar). For that purpose cells of molybdenum and molybdenum‐rhenium‐alloys were developed which allow the simultaneous measurement of ρ, σ, andS.The experiments were performed in an internally heated pressure vessel containing argon as pressure transmitting medium. ‐ A model of hard spheres immersed in a uniform background potential was found to give a fair description of thep‐V‐Tdata, for densities larger than the metal‐nonmetal‐transition‐density, i. e. for densities between 1.4 and 0.7 g/cm3. A modified Van der Waals equation of state with only two adjustable parameters was developed which fits the experimental data between 1.4 and 0.7 g/cm3. Effective hard‐sphere diameters were determined by using the experimental values of the t

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830305

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractDie Reaktion von H‐Atomen mit Hydroperoxylradikalen wurde in zwei isothermen Strömungssystemen untersucht. Der Nachweis der HO2‐und OH‐Radikale erfolgte mit der Methode der Laser‐Magnetischen‐Resonanz. Die HO2‐Radikale warden entweder in der Reaktion H + O2+ M → HO2+ M (Strömungssystem (A)) oder in der Reaktion F + H2O2→ HO2+ HF (Strömungssystem (B)) erzeugt. Das Trägergas war Helium bei einem Gesamtdruck von 500–800 Pa(A)bzw. 130 Pa(B). ‐ Die Geschwindigkeitskonstantek2=k2a+k2b+k2cder Gesamtreaktion:ergibt sich einmal aus der Messung der quasistationären [HO2]‐Konzentration (A) und zum anderen direkt aus der Messung des [HO2]‐Konzentrations‐Zeit‐Profils in An‐ und Abwesenheit eines H‐Atomüberschusses (B). Der Wert der Geschwindigkeitskonstante beträgt:Simulationen der [OH]‐ und [HO2]‐Konzentrationsprofile in dem System H + O2+ M bestätigen den gemessen

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830306

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractNitrogen dioxide (1.3 · 10−4, 4.0 · 10−4, and 7.2 · 10−4mol/l) has been photolysed (λ = 366 nm) at room temperature in the presence of ethylene (3.7 · 10−2mol/l). Quantum yields of N2O, NO, CO, CO2, O2, CH2O, (CH2)2O, CH3CHO, CH3ONO, CH3ONO2, CH3NO2, C2H5ONO2, and C2H5NO2were determined (NO2actinometry). Satisfactory N, O, and H material balances were obtained. ‐ The O atoms from the photolysis of NO2react with NO2to give NO3*, as well as with ethylene to yield C2H4O*. It is concluded that the excited NO3*, rather than being deactivated to thermal NO3, essentially reacts chemically with ethylene. The excited C2H4O* may either become collisionally deactivated into (CH2)O and CH3CHO, or decay to CHO and CH3radicals. The observed products can be explained via subsequent reactions of these radicals. A number of rate constants and ratios of rate constants pertinent to this system have

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830307

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractThe photolysis of pure N2O and of N2O in a large excess of He at 184.9 nm and at 206.2 nm was used as a source of O(1D) atoms, to study the branching ratio of reactions (2a) N2O + O(1D) → N2+ O2and (2b) N2O + O(1D) → NO + NO, as function of kinetic energy of O(1D). The mole fractionb=k2b/(k2a+k2b) of O(1D) atoms reacting with N2O via (2b) governs the source strength of NO in the stratosphere. The products N2, O2, and NO were measured every 3 minutes by automated gas chromatography, and continuously by a chemi‐luminescence detector as function of time during the photolysis of N2O. Back extrapolation of the product ratios to zero conversion yielded the correct stoichiometry. The value ofbderived from initial product ratios wasb= 0.617 ± 0.015, independent of kinetic energy in the range 11.3 to 184 kJ/mol. The result is in excellent agreement with a theoretical model of reaction (2) proposed by Tully. The new value ofb= 0.617 increases the source strength of NO in the stratosphere by 23% relative to current model calculations based onb

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830308

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractThe photoelectrochemical behaviour of several reagents at the SrTiO3anode has been investigated. Current‐doubling was found with several reducing agents. By competitive reaction experiments, hole capture was detected with some other reagents. Quantitative data on relative hole reactivities were obtained for several reducing agents, including water. The position of the band edges at the semiconductor surface was deduced from capacitance measurements. The reactivity data are interpreted in terms of the position of electron energy levels at both sides of the surface, and the applicability of the direct electron transfer model to the reactions observed is discusse

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830309

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractA comparative study was made on the photocurrent of etched and mechanically polished n‐GaAs single crystal electrodes. The photocurrent was investigated as a function of voltage, light intensity and wavelength. The results indicate that polishing creates defects which act as recombination centres. Spectral response measurements yield information on the spatial distribution of the defects involved and on the diffusion length of the hole

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830310

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY

摘要:

AbstractHigh temperature phase equilibrium data are compiled from the literature for the Mn—Co—O, Fe—Mn—O, and Fe—Co—O systems. These data are then analyzed with a view to examining the thermodynamics of the spinel phases. It is shown that the results are consistent with a simple “ideal” model of cation distribution in the spinel phases. The representation and subsequent analysis of the phase equilibria are greatly facilitated through the use of isothermal logpo,‐composition phase diagrams and through the use of a computer program to calcula

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830311

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1979

数据来源: WILEY