摘要:

AbstractThe complex coordinate method combined with the Floquet‐Bloch theory has the advantage of treating the metastable quasi‐energy states (i.e., resonances) of time‐periodic Hamiltonians in terms of bound state formalism. The formalism derived here is a general one. It enables one to use complex basis functions when needed and to calculate the resonance positions and widths foranytime‐periodic Hamiltonians. A numerical example is given to illustrate the potential use of the proposed method in the study of the dynamics of laser‐driven systems and of time‐periodic classical chaotic H

ISSN:0021-2148    

DOI:10.1002/ijch.199000011

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractPhotoinitiated H + CO2→ OH + CO reactions are discussed, with emphasis on reactions in CO2HI complexes. Under single‐collision bulk conditions, reaction probability rises with collision energy by two orders of magnitude throughout the range 10300–19000 cm−1(ΔH= 8960 cm−1). Modest probabilities at collision energies well above threshold are interpreted as due to the inability of the heavier nuclei to move fast enough to trap the H atom on the HOCO potential surface. The pronounced increase in reaction probability with collision energy can be due to impact‐induced distortion of the CO2frame, localizing the H atom in a shallow region of the HOCO potential surface long enough for the heavier nuclei to move toward the HOCO equilibrium geometry, thus capturing the H atom. Measurements of nascent OH(v= 0) R, T excitations indicate a significant bias toward product translation and away from OH rotation at the highest collision energies. OH LIF spectra taken at different collision energies provide a map of nascent OH(v= 0) rotational excitation for different values ofE†, the HOCO†energy in excess of the OH + CO product channel. With CO2HI complexes, pairwise I‐H and H‐CO2repulsions before HOCO†is formed increase the I‐HOCO†speed at the expense of HOCO†internal excitation. It is pointed out that with CO2HBr, the Br atom is 3.6 Å from the C atom along a line perpendicular to the CO2axis, with the H atom localized near one of the O atoms. CO2HI is expected to be qualitatively similar. The OH(v= 0) rotational distribution obtained using 239‐nm photolysis of CO2HI complexes differs markedly from that obtained under single‐collision conditions at the same photolysis wavelength, the former being colder and qualitatively distinct from any of the OH(v= 0) distributions obtained at a single collision energy. The OH(v= 0) rotational distribution obtained using CO2HI complexes can be reconciled with a bimodalP(E†) distribution (e.g., ∼ 30% atE†∼ 800 cm−1and ∼ 70% atE†∼ 6000 cm−1). The 6000‐cm−1component is attributed to the squeezed‐atom effect (E†= 7880 cm−1for single‐collision conditions at the same photolysis wavelength), while the origin of the other component is uncertain. It may derive from (i) mechanisms that produce HOCO†with lowE†values, (ii) mechanisms that relax HOCO†and/or OH such as inter

ISSN:0021-2148    

DOI:10.1002/ijch.199000012

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAfter twenty years, the theory of radiationless transitions in molecules is reviewed. Its qualities and its strengths are discussed. It is pointed out, however, that this theory does not explain properly the quantum yield for nonresonant excitation, which should approach unity for large values of detuning. Insertion of an intermediate state remedies this situation and leaves the theory largely unaffected. The requirement of an intermediate state may explain the rather arbitrary variation of quantum yields among organic molecules and it may also be responsible for the rather too large number of interacting states observed in a high‐resolution molecular eigenstate spectru

ISSN:0021-2148    

DOI:10.1002/ijch.199000013

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractTwo‐color charge transfer transitions are developed as a probe of intermolecular potentials, electronic relaxation, and photodissociation dynamics of halogens in condensed rare gases. Two illustrative examples are given: electronic relaxation of Br2in liquid Xe and recombination dynamics of Cl atoms in high pressures of Xe. The Br2A(3π1+u) and A'(3π2+u) states, which are in fast equilibrium, are not quenched by the solvent in liquid Xe. In dilute solutions, they relax radiatively via the A' state with a lifetime of ∼ 100 μs. In concentrated solutions, diffusion‐controlled self‐quenching of Br2(A/A') proceeds with a probability of 0.07 per encounter. An encounter is found to be equivalent to four gas kinetic collisions. The photodissociation of Cl2and recombination of Cl atoms in gaseous Xe, 1–55 atm, are studied. The recombination kinetics is well reproduced by incorporation of diffusion‐controlled encounter frequencies in the rate constants. An equilibrium constant for formation of XeCl(X) of 2.3 × 10−22cm3is derived from the

ISSN:0021-2148    

DOI:10.1002/ijch.199000014

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA systematic study of the mass spectra of particles formed in a supersonic nozzle expansion of Zn, Cd, and Hg vapors together with Na was performed. The particles discussed in this paper contain only one heavy atom and less than 12 Na ligands. Mass spectra from the neutral particles were generated by photoionization at five wavelengths (250, 260, 280, 300, and 320 nm) with a slit width corresponding to 16.5 and 3.3 nm, respectively. The abundances were corrected to relative differential ionization cross‐sections. Photoionization potentials for NanM with 5

ISSN:0021-2148    

DOI:10.1002/ijch.199000015

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractQuasi‐classical trajectory calculations have been performed to investigate the dynamics of the H + HX → H2+ X reactions, where X = Cl, Br, and I. Calculations were performed for two collision energies, 16 and 36 kcal mol−1. The results show that the dynamics of the abstraction reactions at these high collision energies are rather unusual. The product energy and angular distributions can be accounted for by a mechanism that involves an isolated interaction between the two H atoms in the system to form H2followed by hard‐sphere scattering of this newly formed H2off the

ISSN:0021-2148    

DOI:10.1002/ijch.199000016

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe kinetics of surface chemical reactions depend critically on the lateral distribution of the adsorbed reactants. In some cases, the adsorbates are aggregated into islands and the rate of reaction is strongly influenced by the structural (sizes and shapes) and energetic (lateral interaction potentials) characteristics of the aggregated overlayer. Adsorbate aggregation or segregation on surfaces may be induced by a variety of mechanisms, three important types of which are briefly discussed here. The first process is driven by strong lateral interactions between the adsorbed particles, which favor their organization in an ordered two‐dimensional phase, but because of kinetic constraints the system only reaches a long‐lived metastable state characterized by finite islands with highly ramified edges. A somewhat more complex aggregation‐segregation process, in a system comprised of two interacting adsorbate species, is also described, and the consequences with respect to surface reaction kinetics are demonstrated. The second aggregation process reflects (Eden‐type) island formation during adsorption of molecules from the gas phase. More specifically, these islands result from the so‐called (extrinsic) precursor‐mediated chemisorption mechanism. Finally, we discuss the segregation of adsorbed reactants induced by the bimolecular annihilation reaction A + B → 0, under steady‐state conditions. Unlike in the first example, this segregation process takes place even in the absence of adsorbate interactions (except for the reactive A‐B interaction) and is most pronounced in the absence of p

ISSN:0021-2148    

DOI:10.1002/ijch.199000017

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA scheme is discussed for real‐time observation of a finite vibrational motion of diatomic molecules. Observation schemes based on the Franck‐Condon principle, i.e., the “persistence” of a coordinate wave packet in an ultrashort excitation, are p

ISSN:0021-2148    

DOI:10.1002/ijch.199000018

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractPulsed Doppler‐free two‐photon excitation of single rotational states of the 141vibronic state of benzene with a resolution of 70 MHz is employed to investigate the influence of molecular rotation on the decay behavior of these states. The analysis of the completely resolved (Δv= 15 MHz) spectrum of the 1410band, measured with a CW laser, makes it possible to specify whether individual states are perturbed by other (“dark”) S1states and allows the precise determination of the degree of admixture of these background states. The vibrational identity of the background states is known from emission spectra of single rovibronic states. Unperturbed rovibronic states were investigated up toJ'K'=6761, and a pure exponential decay was found which does not depend on molecular rotation in accord with a nonradiative decay of S1benzene in the statistical limit. The decay of perturbed states, which was also found to be purely exponential, depends strongly on the degree of admixture of the background state and on its vibrational identity. Values of the decay time of two identified “dark” zero‐order S1vibrational states, which cannot be directly excited by optical transitions, are determined by evaluation of the decay behavior of the pe

ISSN:0021-2148    

DOI:10.1002/ijch.199000019

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe possibility for nonstatistical reaction dynamics is explored with special reference to many‐atom systems. Starting with the early example of photoselective processes in van der Waals molecules, we consider other examples where the same physical mechanism may apply due to similar or other chemical reason

ISSN:0021-2148    

DOI:10.1002/ijch.199000020

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY