ISSN:0005-9021    

DOI:10.1002/bbpc.19900941002

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

年代:1990

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941003

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

年代:1990

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941004

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

年代:1990

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941005

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

年代:1990

数据来源: WILEY

摘要:

AbstractMany technologically interesting materials properties are caused by intrinsic structural or dynamic disorder phenomena in solids. For this reason, the structural characterization of disordered states constitutes a central aspect of materials science. Within the past decade, nuclear magnetic resonance techniques have made increasingly significant and detailed contributions to this subject. The present review will portray some of the more common methods employed and discuss several important applications to problems in various inorganic materials areas.

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941006

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

年代:1990

数据来源: WILEY

摘要:

AbstractNegative ions up to masses>3 · 103u in fuel‐rich and sooting premixed low‐pressure acetylene/oxygen flames have been analyzed by means of a time‐of‐flight mass spectrometer. This work deals with the quantitative analysis of ions up to masses of 200 u, but the larger polyhedral carbon ions, which were negative charge carriers in the soot forming zone, are not considered here. Concentration profiles of ca. 50 different ions and the dependence of maximum ion concentrations on the C/O ratio are reported. ‐ Ions in the preheating zone were anions of carbonic acids and diacids which contained oxo, keto and peroxy groups. With increasing height in the flame these anions decomposed by decarboxylation and dissociative electron detachment. At higher temperature in the oxidation zone, polyynides (C2nH−), linear polycarbon ions and higher ketenides (CmHO−) prevailed. The polyynides were in chemical equilibrium with acetylene and higher neutral polyynes. Enthalpies of formation (referenced to that of C2H−, 274 kJ/mol) were determined for C4H−(414), C6H−(603), C8H−(810) and C10H−(1025 kJ/mol). Possible reaction mechanisms for the formation of the acid anions and the ketenides are discussed. Negative polycyclic aromatic hydrocarbon ions were completely missing in acetylene flames, in contrast to their occu

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941007

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe insertion reaction of singlet methylene CH2(ã1A1) into the strongest element‐hydrogen bond, H‐F, is investigated. CH2(ã1A1) is generated by pulsed UV‐laser photolysis of CH2CO. Its removal is directly monitored via LIF‐detection. The experiments are carried out under first order reaction conditions at temperaturesT= 295, 380, and 485 K. Second order rate constants are determined from plots of first order rate constants versus the partial pressure of HF. The expressionk1= (5.5 ± 1.5)·1013·(T/295 K)(‐0.5±0.5)cm3/mol s is derived for the rate constant of the total depletion of CH2(ã1A10,0,0) with HF. Thus at room temperature the reaction is slower than the analogous reactions with NH3, H2O and HCl. For the isotopically substituted CD2(ã1A10,0,0) with HF the following rate expression is determined:k2= (1.0 ± 0.3)·1014(T/295 K)(‐1.0±1.0)cm3/mol s. The reaction of vibrationally excited CH2(ã1A10,0,0) with HF has a room temperature rate constant ofk3= (2.0 ± 0.4)·1014cm3/mol s. Fluorocarbene CHF is detected as primary reaction product by LIF. Thermochemical considerations show the formation of CHF is the only exothermic reaction pathway besides physic

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941008

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

年代:1990

数据来源: WILEY

摘要:

AbstractLifetimes of1Δgsinglet oxygen (1O2) have been determined in 12 solvents in dependence of pressure and in part of temperature using time resolved phosphorescence techniques. Experimental activation volumes for the deactivation of1O2by solvent molecules vary between ‐11.9 (pentane) ≤ ΔV#obs≤ ‐4.1 ml mol−1(formamide) at 298 K. The increase of ΔV#obswith temperature was measured in toluene and CH3CN. The data are analyzed by means of a kinetic scheme assuming a preequilibrium of1O2and solvent molecule to form a singlet contact complex1C. Deactivation of1O2occurs by energy transfer between the collision partners of C converting1C to3C, which subsequently splits into the deactivation products. A statistical model developed by Yoshimura and Nakahara is used to calculate the reaction volumeΔVcof the preequilibrium. It is revealed that the major part ofΔV#obs, consists ofΔVc. Activation volumesΔV#Eof the actual deactivation of1O2by oscillators X–Y of the solvent molecule depend neither on the polarities of solvent nor of X–Y. Independent of oscillator they are estimated to beΔV#E≈ −2 ml mol−1if X–Y

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941009

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe following work gives a discussion on hydrogenated amorphous silicon (a‐Si:H) film preparation by laser induced chemical vapor deposition (LICVD) using a pulsed CO2‐laser in a parallel configuration. Deposition rate and initiation of polymerization were studied as a function of total pressure, gas flow, gas mixture (buffer gas, silane and/or disilane), substrate temperature, and radiation flux. The results lead to a reaction model where higher silane homologues play an important role for the film production. The film properties strongly depend on the substrate temperatureTs. The activation energyEaof the dark conductivity decreases from 1.1 eV to 0.7 eV for films prepared atTs= 230°C to 450°C. In the same temperature range, the dark conductivity σdincreases from ∼10−14to ∼10−10(Ω cm)−1, whereas the photo conductivity σphshows a maximum of ∼10−6(Ω cm)−1atTs= 320‐330°C. These values, especially their temperature behaviour, are compared with the results of other CO2‐LICVD works and further production methods. It is shown that the film formation depends on the gas phase chemistry as well a

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941010

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe79Br and127I nuclear quadrupole resonance spectra of para‐substituted anilinium bromides and iodides 4‐RC6H4NH⊕3X⊖with X = Br, I and R = Cl, Br, SCN, OCH3were studied in the temperature range 77 ≤T/K≤ 420. 4‐ClC6H4NH⊕3Br⊖shows a phase transition atTc= 132 ± 1 K. 4‐ClC6H4NH⊕3Br⊖as well as 4‐BrC6H4NH⊕3Br⊖exist as hemihydrates, too. The two hemihydrates are isomorphous, crystallizing monoclinic, C52h‐ P21/c, Z = 8. 4‐ClC6H4NH⊕3Br⊖·1/2 H2O:a= 1370.9(5) pm,b= 789.1(3) pm,c= 1940.1(7) pm, β = 125.38(1)°; 4‐BrC6H4NH⊕3Br⊖· 1/2 H2O:a= 1380.1(7) pm,b= 794.8(5) pm,c= 1934.2(9) pm, β = 125.11(1)°. The influence of hydrogen bonds on79Br NQR is investigated. NQR results and the structures of the studied compounds are discussed in comparis

ISSN:0005-9021    

DOI:10.1002/bbpc.19900941011

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

年代:1990

数据来源: WILEY