ISSN:0005-9021    

DOI:10.1002/bbpc.199000001

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

年代:1990

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.199000002

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis review serves as an introduction to the main topic of the Bunsentagung 1990. Representative examples of elementary chemical reactions in gases and in the gas‐liquid transition range are discussed and illustrated with respect to their temperature, pressure, and solvent dependence

ISSN:0005-9021    

DOI:10.1002/bbpc.199000003

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe role of the divalent nature of barium atoms in chemical reactivity was explored using crossed molecular beams. Angular and velocity distributions of products from reactions of Ba(1S) with NO2and O3indicate the existence of long lived collision intermediates despite very large reaction exothermicities. The existence of these intermediates results from barriers to transfer of the second electron necessary to form ground state products. Although BaO was the dominant product in both reactions, two previously unknown channels were observed: Ba + N02→ BaON + O and Ba + O3→ BaO2+ O. We obtained bond dissociation energies ofD0(Ba–ON) = 270 ± 80 kJ/mol andD0(Ba – O2) = 500 ± 80 kJ/mol for these molecules. The dependence of the cross sections for the ion channels, Ba(1P) + Cl2→ Ba++ Cl−2and Ba(1P) + Cl2→ BaCl++ Cl−on Ba(1P) orbital alignment and collision energy was used to probe the course of the reaction through intersections between the ionic and covalent potentia

ISSN:0005-9021    

DOI:10.1002/bbpc.199000004

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

年代:1990

数据来源: WILEY

摘要:

AbstractChemists are continuously facing questions and problems as follows: Is it possible to direct the course of a reaction according to one's intentions? Is the activation of specific bonds that are either remote or adjacent to a functional group feasible? What factors dictate the different behaviour of transition‐metal ions in their reactions with organic substrates? Answers to these and other questions are provided by studying the gas‐phase chemistry of “naked” first‐row transition‐metal ions with aliphatic nitriles and some other simple organic substrates. By systematically modifying both the organic molecules and the metal ions, a quite detailed insight is achieved into the mechanisms that are operative, and knowledge is accumulated which permits to specify the conditions that are to be met in order to bring about specific processes. “Remote functionalization”, the generation of ion/dipole intermediates, and the formation of multi‐ligated metal‐ion alkene complexes turn out to be the most important mechanisms in the reactions of aliphatic nitriles with transition‐metal ions in the gas phase. In addition, results will be presented which point to degenerate isomerizations involving metallacycles as intermediates. We will also demonstrate thatdirectCC bond activation prior to CH bond activation can be achieved, a process for which no analogue exists in solution chemistry. The studies have been performed by using tandem mass spectrometry techniques in a sector‐field mass spectrometer as well as ion/molecule reactions in a Fourier transform ion cyclotron reson

ISSN:0005-9021    

DOI:10.1002/bbpc.199000005

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

年代:1990

数据来源: WILEY

摘要:

AbstractWith new laser techniques and with gas phase and molecular beam experiments, ist is now possible to tetermine the ultrafast motion in isolated chemical reactions – chemistry on the 10−13‐second time

ISSN:0005-9021    

DOI:10.1002/bbpc.199000006

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

年代:1990

数据来源: WILEY

摘要:

AbstractBy the technique of Stimulated Emission Pumping (SEP), single high‐lying rotation vibration states of CH3O (X̃2E) with defined total energyErrand total angular momentumJwere probed in the regime 3000 cm−1≤Err≤ 9300 cm−1, up to well above the H – CH2O asymptotic dissociation limit (≈ 6800 cm−1). Observed low resolution SEP spectra exhibit distinctive vibrational band structure. Spectra recorded at high resolution reflect intramolecular dynamical processes occuring on different time scales. The detailed spectroscopic characterization of the level structure of highly excited CH3O provides the basis for critical tests of models for unimol

ISSN:0005-9021    

DOI:10.1002/bbpc.199000007

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

年代:1990

数据来源: WILEY

摘要:

AbstractRate constants have been measured for the reaction of the light hydrogen isotope muonium with benzene and 2,3‐dimethylbutadiene‐1,3 in the gas phase and in several solvents. Comparison with H atom data reveals (1) appreciable kinetic isotope effects, (2) a strong contribution of tunnelling for the activated reaction with benzene, (3) encounter controlled reaction for Mu addition to the diene, (4) a mass dependence of the diffusion constant of hydrogen isotopes in solution, and (5) an enhancement of the rate constant in solution over that in the gas phase by a factor, except for water, of the inverse Ostwald solubility coefficient for hydrogen. The isotope‐dependent reduction of the solvent effect in water is tentatively ascribed to the dynamics of the clathrate‐like structure when the hydrogen atom

ISSN:0005-9021    

DOI:10.1002/bbpc.199000008

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

年代:1990

数据来源: WILEY

摘要:

AbstractResults of experimental investigations on the thermal rate constants and the microscopic dynamics of the hydrogen exchange reaction, including the isotopic variants and the spectroscopy of the H3‐complex, are compared with recent predictions based on quasi‐classical, approximate and exact quantum, and variational transition state theory calculati

ISSN:0005-9021    

DOI:10.1002/bbpc.199000009

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe rotational relaxation of t‐stilbene and t‐diphenylbutadiene in the first electronically excited singlet state was measured by picosecond anisotropic absorption spectroscopy. The viscosity η in n‐alkane solvents was changed by increasing the pressure up to several kilobars. In all cases the viscosity dependence of the rotational relaxation time τorcould be described by a modified form of the Stokes‐Einstein‐Debye equation. No solvent dependence was found for η ≤ 0.8 cP. Therefore we attribute the observed solvent dependence of photoisomerisation rates of t‐stilbene and t‐diphenylbutadiene measured under the same conditions to specific solvent‐solute interactions that modify the path on the pote

ISSN:0005-9021    

DOI:10.1002/bbpc.199000010

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

年代:1990

数据来源: WILEY