ISSN:0021-2148    

DOI:10.1002/ijch.199000001

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractWe present a general theory of the photodissociation of diatomic molecules to the hyperfine sublevels of open‐shell atomic fragments. The hyperfine interactions affect the fragment hyperfine sublevel populations, polarizations, etc., either when the fragment atomic hyperfine sublevels are optically resolved, when resonances possess hyperfine splittings, or both. The case of hyperfine splittings in resonances is of particular interest for states whose principle parentage is singlet, but which exhibit hyperfine splitting due to nonadiabatic mixing with close‐lying triplet states. Such resonances have been observed in the photodissociation of SiH+(Sarre, P.J. et al.,Phil. Trans. R. Soc. London, 1988,A324: 233). We also show how our nonadiabatic theory in the presence of hyperfine interactions reduces to the general theory of diatomic photodissociation to open‐shell atoms of Singer et al. (J. Chem. Phys., 1983,79: 6060) when resonance hyperfine splittings or hyperfine structure states of the fragments are not resolved in particular experi

ISSN:0021-2148    

DOI:10.1002/ijch.199000002

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractRecently, we have developed an experimental method for the detection of triplet states generated by laser excitation in supersonic beams. It is based on electron ejection from low work‐function surfaces by metastable triplet states. We have detected both directly laser‐excited triplets and triplets generated via intersystem crossing from laser‐excited singlet states. Here, we review the applications of this method and discuss its mechanism. By comparing the laser‐induced fluorescence (LIF) spectrum and Surface Electron Ejection by Laser‐Excited Metastables (SEELEM), we have measured relative triplet formation quantum yields for several aromatic compounds. By utilizing a detector mounted on a translational stage, we could vary the distance between the pulsed laser excitation and the detector and measure the decay rates of triplets in molecular beams. The major advantage of the method is in extending the measurement of triplet lifetimes to the ∼ 1‐ms range. The combination of LIF, SEELEM, and fluorescence quantum yields enabled us to discriminate between intersystem crossing and internal conversion in isoquinoline. SEELEM is now being utilized in studying the spectroscopy and the dynamics ofdirectlylaser‐excited triplet states. Although the oscillator strength of the lowest triplet state of pyrazine is about 10−8, we have measured the spectrum and the decay rates of its various vibronic levels. Our results support the notion that surface Penning ionization is the mechanism of SEELEM. The detector is insensitive to vibrational energy (thus enabling the distinction between intersystem crossing and internal conversion). The detection sensitivity of triplets rises with the excesselectronicenergy and with the lowering of the surf

ISSN:0021-2148    

DOI:10.1002/ijch.199000003

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA brief review of recent developments in the theory of unimolecular reactions is presented, with emphasis on the work carried out at The University of Chicago. The subjects considered are: the development of a paradigm for the control of selectivity of a photoinduced reaction; the development of an alternative form for the classical mechanical theory of the rate of a unimolecular reaction; the beginnings of an understanding of the influence of classical mechanical chaos on the corresponding quantum‐mechanical description of an unbounded system; and the possible decoupling of a part of anN‐degree‐of‐freedom system from the rest of the system on a time scale of interest with respect to subsystem internal energy transfer and chemical reaction. The intellectual linkages between these subjects are very briefly s

ISSN:0021-2148    

DOI:10.1002/ijch.199000004

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSome of the tantalizing puzzles regarding clusters are described. Some specific results concerning the dynamical behavior of clusters of particular sizes and having various potentials are described, to give some insight into the relationship between the form of a potential and the kind of behavior it yields. Solid‐liquid, solid‐soft solid, surface melting, and a remarkable single “subsurface layer mobility” all can be found in particular in

ISSN:0021-2148    

DOI:10.1002/ijch.199000005

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of electronic structure on bridge‐assisted electron transfer are considered. Using static perturbation theory, time‐dependent perturbation theory, and direct time‐dependent dynamics within generalized tight binding models, we examine the role of energy gaps, relative energetics of donor and acceptor orbitals with hole‐type and electron‐type superexchange sites, damping and dephasing, and overall energetics in electron transfer. We find that a generalization of the simple McConnell relationship to nonresonant transfer can in fact be made, but that no simple formula describes all limits; this is important in applications to a number of systems, including photosynthetic reaction centers, in which such superexchange occurs. The dynamical studies indicate some important and unexpected phenomena: these include quantum interferences between different pathways, recurrences and oscillations, and competitive effects of hole‐type and electron‐type superexchange. We suggest that direct dynamical study, as has begun to appear from several laboratories, provides an excellent way to visualize the intermediate state contributions to intramolecular electron trans

ISSN:0021-2148    

DOI:10.1002/ijch.199000006

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractFor a wide range of substances, extending well beyond the regime of corresponding states behavior, the contour in the temperature‐density plane along which the compressibility factorZ = P/ρkTis the same as for an ideal gas is nearly linear. ThisZ= 1 contour, termed the Zeno line, begins deep in the liquid region and ascends as the density decreases to the Boyle point of the supercritical fluid, specified by the temperatureTBfor which (dZ/dρ)T=0 as ρ → 0; equivalently, atTBthe second virial coefficient vanishes. The slope of theZ= 1 line is —B3/(dB2/dT), in terms of the third virial coefficient and the derivative of the second, evaluated atTB. Previous work has examined the Zeno line as a means to extend corresponding states and to enhance other practical approximations. Here we call attention to another striking aspect, a strong correlation with the line of rectilinear diameters defined by the average of the subcritical vapor and liquid densities. This correlation is obeyed well by empirical data for many substances and computer simulations for a Lennard‐Jones potential; the ratios of the intercepts and slopes for the Zeno and rectilinear diameter lines are remarkably close to those predicted by the van der Waals equation, 8/9 and 16/9, respectively. Properties of the slightly imperfect fluid far above the critical point thus implicitly determine the diameter of the vapor‐liquid coexistence curve below the cr

ISSN:0021-2148    

DOI:10.1002/ijch.199000007

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIntramolecular electron transfer (ET) processes with the main energetic contributions coming from the solvent reorganization are investigated for a polar medium that exhibits dynamic disorder. Dynamic disorder provides a description of the anomalous relaxational behavior of correlation functions in complex glass‐like systems, alternative to static disorder. In particular, the questions addressed are whether time‐resolved observation of nonexponential ET in such a medium can readily distinguish experimentally between static and dynamic disorder and whether a contribution of intramolecular degrees of freedom to the ET can be identified by

ISSN:0021-2148    

DOI:10.1002/ijch.199000008

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe Coulomb Explosion Imaging (CEI) method was used to determine the structure and photochemistry of carbon clusters. The cyclic structure of C4was found using a combination of laser photodetachment techniques and the CEI method. The cyclic C4electron affinity was found to be 2.1 ± 0.1 eV, more than 1 eV lower than the electron affinity of the linear isomer

ISSN:0021-2148    

DOI:10.1002/ijch.199000009

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIn this paper, we review quantum simulation methods for studies of coupled quantum‐classical systems and their applications in investigations of dynamics, spectra, and relaxation phenomena of excess electrons in polar molecular and ionic cluster

ISSN:0021-2148    

DOI:10.1002/ijch.199000010

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY