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AbstractAbstract

[en] The diversity of radiationless processes, e.g. inelastic collisions, electronic-vibrational relaxation, deexcitation, energy transfer, are unified by considering a system, molecular or solid, divided into two subsystems; one characterized as ''''fast''; the other, as ''slow''. Thus, the adiabatic (Born-Oppenheimer) approximation can be applied and partially separates the eigenstates of the two subsystems. These are frequently the electronic states and vibrational levels, but for some processes are local modes (vibrons) and normal modes (phonons). Most radiationless processes are characterized by the irreversible degradation of a single large quantum of the ''fast'' subsystem into many small quanta of the ''slow'' subsystem, however, the inverse occurs in special cases, for example thermal excitation and anti-Stokes emission. The calculation of radiationless transition probabilities is difficult mainly because, in contrast to radiative transitions, the operator coupling the two subsystems is not simple, the static (Condon) approximation to the ''fast'' eigen functions is not valid, and the origin of the irreversibility is often not obvious. The methods of calculation are reviewed; and current trends, emphasized. The trends include: (a) non-Condon analyses, (b) attention to collective effects, (c) novel phenomenological theories, and (d) detailed calculations on specific materials. A glossary of terms used in publications on radiation less processes and a bibliography of theoretical studies thereon are included

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Source

Di Bartolo, B; p. 1-37; 1980; p. 1-37; Plenum Publishing Corp; New York, NY; NATO advanced study institute on radiationless processes; Erice (Italy); 18 Nov - 1 Dec 1979

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Book

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Conference

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AbstractAbstract

[en] The distance dependent lifetime of biacetyl separated from a Ag(111) crystal by NH

_{3}spacer layers ranging in thickness from 28 to 457 A has been measured. We extended previous work, where the molecular emission was resonant with the silver interband/plasmon transition, to the case where the emission is below the interband transition. The modulation of the radiative rate is described inadequately by the classical theory for our experimental geometry. At short distances where nonradiative energy transfer to the metal is important, the classical prediction deviates from the data as well. These observations are consistent with a model in which energy is transferred to electrons localized at the metal surface but might also be explained by an inability of the classical theory to model the radiative rate properlyPrimary Subject

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Journal Article

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Journal of Chemical Physics; ISSN 0021-9606; ; v. 82(1); p. 541-547

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AbstractAbstract

[en] The calculated results of multiphonon non-radiative transitions probability factors I(ε) are presented by both of Huang Kun's statistical distribution theory of phonons and rigorous formula at finite temperature with six-frequency model. These results show that both of them are very consistent at weak coupling under any temperature. However, the remarkable deviation between statistical I(ε) and rigorous I(ε) will appear at strong coupling, high temperature. Moreover, the deviation will increase with the rising of temperature. In addition, the I(ε) is highly sensitive with the variation of Huang-Rhys factor. In particular, it has a region of maximum value for a proper coupling strength

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Journal Article

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Acta Scientiarum Naturalium Universitatis Pekinensis; ISSN 0479-8023; ; CODEN PCTHAP; v. 28(5); p. 622-630

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AbstractAbstract

[en] The influence of changes in geometry of promoting vibrational modes (due to transitions between electronic states) on the rate constants for radiationless transitions in molecular systems has been analysed. It has been demonstrated that in many-promoting-modes model systems, effects due to interferences between different participating modes can greatly modify the magnitudes of rate constants for radiationless transitions as well as the magnitude of the isotope (deuterium) effect. (author)

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Journal Article

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Acta Physica Polonica. Series A; ISSN 0587-4246; ; v. 56(4); p. 535-541

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AbstractAbstract

No abstract available

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Source

5. international conference on high pressure physics and technology; Moscow, USSR; 26 - 31 May 1975; Summary form only.

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Journal Article

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Conference

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High Temperatures - High Pressures; v. 8(6); p. 607-609

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AbstractAbstract

[en] Radiationless transitions of molecules accompanied by a large nuclear rearrangement were investigated. A general formula which includes interference effects among promoting modes was used. Numerical analysis for the model system revealed that the energy-gap dependence of the transition probability exhibits quite different behavior from the usual gaussian-type dependence. (orig.)

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Journal Article

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Numerical Data

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Chemical Physics Letters; ISSN 0009-2614; ; v. 77(2); p. 427-431

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AbstractAbstract

[en] Radiationless decay rates have been measured for the

^{4}Tsub(2g) →^{4}Asub(2g) transition of chromium(III) incorporated into a variety of glass hosts. A discrepancy in the^{4}Tsub(2g) behavior between crystals and glasses point to Cr(III) site symmetry as a key factor in the radiationless decay. (orig.)Primary Subject

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Journal Article

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Chemical Physics Letters; ISSN 0009-2614; ; v. 74(3); p. 404-408

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AbstractAbstract

[en] A suitable extension of the Mori theory to deal with non-hermitian hamiltonians leads to a rigorous justification of models of 'reduced' kind for radiationless decay phenomena. By using the model of an excited state sequentially coupled to two dissipative quasicontinua it is shown that the generalized theory leads to a reduced model consisting of only two 'virtual' states. The standard Mori approach, on the contrary, would result in a chain of more than two states (probably an infinite number of states). It is shown, furthermore, that the biexponential decay behaviour can rigorously be justified in two different ways. The first model only consists of couplings of intramolecular type. The second model also involves an external thermal bath. The generalized Mori theory, when applied to the second model leads to a non phenomenological justification for the kinetic scheme. It is shown, furthermore, that excitations by strong radiation fields result in a different decay behaviour according to whether the former or the latter scheme is applied. (orig.)

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Journal Article

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Advances in Molecular Relaxation and Interaction Processes; ISSN 0378-4487; ; v. 21(2); p. 131-149

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AbstractAbstract

[en] We examine one important (and previously overlooked) aspect of well-known crossing diabatic potentials or Landau-Zener (LZ) problem. We derive the semiclassical quantization rules for the crossing diabatic potentials with localized initial and localized or delocalized final states, in the intermediate energy region, when all four adiabatic states are coupled and should be taken into account. We found all needed connection matrices and present the following analytical results: (i) in the tunneling region, the splittings of vibrational levels are represented as a product of the splitting in the lower adiabatic potential and the nontrivial function depending on the Massey parameter; (ii) in the overbarrier region, we find specific resonances between the levels in the lower and in the upper adiabatic potentials and, in that condition, independent quantizations rules are not correct; (iii) for the delocalized final states (decay lower adiabatic potential), we describe quasistationary states and calculate the decay rate as a function of the adiabatic coupling; and (iv) for the intermediate energy regions, we calculate the energy level quantization, which can be brought into a compact form by using either adiabatic or diabatic basis set (in contrast to the previous results found in the Landau diabatic basis). Applications of the results may concern the various systems; e.g., molecules undergoing conversion of electronic states, radiationless transitions, or isomerization reactions

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Source

(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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AbstractAbstract

[en] Fluorescence quantum yields (Phi/sub F/) from single vibronic levels (SVL's) of glyoxal have been measured between 1 and 12 mTorr. The zero-pressure extrapolated values of Phi/sub F/ decrease nearly monotonically from 0.58 for the zeroth vibrational level (0

^{0}) to 0.22 for the 2^{1}8^{1}level at E/sub vib/=2126 cm^{-1}. From our values of Phi/sub F/ and the fluorescence decay times (tau/sub F/) measured earlier by Beyer, Zittel, and Lineberger (BZL), the collision-free values of radiative (tau/sub R/) and nonradiative (tau/sub NR/) lifetimes have been obtained. The observed value of tau/sub R/ for the 0^{0}level is 4.1 μsec, as compared to the calculated value of 15 μsec estimated from integrated absorption by BZL. Since the observed values of Phi/sub F/ are considerably greater than what had been estimated earlier, the new values for the nonradiative rate (k/sub NR/) are correspondingly smaller. The out-of-plane deformation mode (ν'_{8}) is most effective as an inducing and promoting modePrimary Subject

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Journal Article

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Numerical Data

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Journal of Chemical Physics; ISSN 0021-9606; ; v. 71(12); p. 5049-5052

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