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1.
H. Hornburger M. Melzig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):173-180
It is shown that predissociation can be perceived as a primary process due to the continuum part of a Morse oscillator potential.
In the model proposed here internal conversion to the ground state is thus not necessarily the primary process of a consecutive
dissociation but may be a simultaneous decay. As a consequence, dissociation rates should show strong variations from specific
(ro-) vibrational states of the first excited electronic states that are similar to those known from “pure” internal conversion
rates. This behaviour is demonstrated by calculating predissociation rates for the process. Especially the out-of-plane modes seem to play an extraordinary role in the excess energy behaviour of the predissociation
rate. At lower excess energies, rates from single vibronic levels with out-of-plane mode characteristics may show an increase
by several orders of magnitude.
Received: 13 November 1998 相似文献
2.
W. Chin M. Mons I. Dimicoli F. Piuzzi B. Tardivel M. Elhanine 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):347-355
By using depopulation laser techniques, like IR-UV population labeling coupled to mass-selected R2PI detection, we confirm
that four tautomers are responsible for the near UV spectroscopy (310-280 nm) of guanine: two enol and two keto forms, each
pair having a 7NH and a 9NH form. Besides the UV spectroscopy of each tautomer, additional information on the excited state
nature and dynamics is obtained from fluorescence studies. In particular, the quenching of fluorescence beyond 285 nm, the
existence of a background absorption, as well as the existence of a strongly red-shifted component in the fluorescence emission
provides evidence for a strong electronic mixing in the excited state together with an efficient non-radiative process. The
details of these features are found to be tautomer-dependent. Comparison of the present results with literature data on other
purine molecules, like adenine or 9-substituted guanines, enables us to propose a new insight on the spectroscopy and dynamics
of the purine molecules. First, a large variability of the tautomer distribution in the gas phase is found within the purine
family, in particular a molecular change, as simple as a 9-methylation on guanine, can reduce the tautomer distribution to
a single species (enol form). Since the absorption spectrum is tautomer-dependent as well as substituent-dependent, it turns
out that the tautomer population is one of the major parameters that control the overall shape of the UV spectrum. Second,
the excited state model, often evoked in the literature, which involves electronic coupling between excited states of different
natures, namely ππ* and nπ* states, might account for the present fluorescence measurements on guanine, providing an extensive excited state electronic
mixing is assumed for these systems.
Received 24 June 2002 Published online 13 September 2002 相似文献
3.
O.-H. Kwon H. Yoo D.-J. Jang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):69-75
While the intercalation of C60 and the formation of C
60
-
in the supercages of NaX and NaY are confirmed by using 129Xe NMR and ESR, the photophysical properties of C60 and C
60
-
are characterized by monitoring transient reflectance spectra and kinetics, fluorescence kinetics, and diffuse reflectance
spectra. C
60
-
is considerably more abundant in NaY than in NaX. This difference is explained in terms of polarity difference between two
zeolites. Both C60 and C
60
-
have remarkably elongated excited-state lifetimes due to their collision-free environment in zeolitic nanocavities although
C
60
-
has much shorter lifetimes than C60. C
60
-
, in particular, shows intense absorption and emission due to its reduced symmetry in zeolites.
Received 13 July 2001 and Received in final form 8 October 2001 相似文献
4.
Summary The room temperature phosphorescence of crystalline thianthren in the 1.6–3.3 eV energy region has been measured using time
delays going from 0.03 to 9.5 ms. The time dependence of the emission spectra which show the presence of three resolved bands,
was analysed by means of a numerical best-fitting procedure, and the results obtained have been compared with those predicted
by means ofab initio and semiempirical molecular orbital calculations. 相似文献
5.
Summary Using a laser-induced fluorescence technique, we have measured lifetimes of CS2 as functions of pressure, collecting the emission at various wave-length regions. We have obtained quenching rate constants
for pure CS2 and CS2 plus CH3CN and CO2 as collision partners. When the emission is collected at a very long wave-length, evidence is given of vibrational relaxation
in the singlet state which leads to the existence of a low-energy pathway of intersystem crossing. Two different long-lived
states are also detected in the wave-length region centred at 5860 ?, one in the low-pressure regime and the other at pressures
above 0.2 Torr approximately. Quenching rate constants of triplet CS2 by CO2 are about the same for both long-lived states, suggesting that vibrational relaxation could occur in the triplet state as
well.
Riassunto Usando una tecnica a fluorescenza indotta da laser, sono state misurate le vite medie di CS2 in funzione della pressione, raccogliendo le emissioni in varie regioni di lunghezza d'onda. Si sono ottenute costanti di spegnimento per CS2 puro e CS2 piú CH3CN e CO2 come associati nella collisione. Quando si registra emissione a lunghezza d'onda molto grande, si prova l'esistenza di rilassamento vibrazionale nello stato di singoletto che porta all'esistenza di un percorso a bassa energia dell'incrocio intersistemico. Sono anche determinati due differenti stati a lunga vita nella regione di lunghezza d'onda centrata a 5860 ?, uno nel regime di bassa pressione e l'altro approssimativamente a pressione sopra i 0.2 Torr. Le costanti di spegnimento del tripletto CS2 mediante CO2 sono quasi le stesse per entrambi gli stati a lunga vita, e ciò suggerisce che il rilassamento vibrazionale potrebbe verificarsi anche nello stato di tripletto.
Резюме Используя технику лазера, возбужденного флуоресценцией, мы измеряем времена жизни CS2, как функцию давления, собирая излучение в различных областях длин волн. Мы получаем постоянные скорости гашения для чистого CS2 и для CS2 плюс CH3CN и CO2, которые участвуют в соударениях. Когда излучение собирается для очень больших длин волн, то отмечается вибрационная релаксация в синглетном состоянии. Были обнаружены два различных долгоживущих состояния с длиной волны при 5860 ?, одно при низком давлении, а другое при давлениях около 0.2 тор. Постоянные скорости гашения триплетного CS2, обусловленные CO2, оказываются примерно одинаковыми для обоих долгоживущих состояний. Этот факт свидетельствует о том, что вибрационная релаксация может иметь место также в триплетном состоянии.相似文献
6.
C. Reylé P. Bréchignac 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):205-210
Fluorescence spectra of naphthalene, C10H8, were obtained in the laboratory under conditions which provide an appropriate simulation of the cometary conditions: super-cooled
gas phase molecules in a collision-free environment. Five spectra were recorded, the excitation energies ranging from 1422
to 5293 cm−1 above the first electronic state S1 at 32 020 cm−1. A comparison with previous jet-cooled naphthalene fluorescence spectra obtained by Beck et al. [1] and Hermine [2] shows that the former results are not consistent with the present ones. Spectra obtained by Beck et al. show weaker intensities at greater wavelengths compared to those obtained by Hermine and ourselves. We also measured the
fluorescence lifetimes by recording the fluorescence decay as a function of time after the excitation of the molecules by
monochromatic lasers and deduced the fluorescence quantum yields. A synthetic emission spectrum under solar irradiation is
obtained for astrophysical implications. 相似文献
7.
B. Soep J.M. Mestdagh S. Sorgues J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):191-203
In the TDMAE molecule (title molecule), the time evolution has been analyzed from the very initial excitation step down to
a fluorescent state, over widely different time scales. Pump probe measurements have been performed at 3 different excitation
wavelengths 400, 266 and 200 nm. The decay has been followed over the femtosecond and subnanosecond ranges with this method
and the decay of the final charge transfer state has been detected by its fluorescence emission. This allows an overview of
the complete decay mechanism. The initial relaxation pathway is interpreted in a similar way to ethylenic molecules, where
the initial wavepacket is quickly trapped in a doubly excited state Z with charge transfer character. Then the Z state decays
slowly (10-100 picoseconds) into the final state. In difference to monoalkenes the final stage of this evolution is a charge
transfer state. The decay of transient Z state to the charge transfer state is a further assessment of the partial ionic character
of the Z state. This type of molecule with low ionization potential can be viewed as a demonstrative example of the interrelation
between the charge induced forces and the deformations in excited state reaction dynamics.
Received 17 January 2001 and Received in final form 23 February 2001 相似文献
8.
T. Käämbre L. Qian J.-E. Rubensson J.-H. Guo C. Såthe J. Nordgren J.-P. Palmqvist U. Jansson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):357-360
The interaction of oxygen with C60 molecules was studied on a C60 film which had been exposed simultaneously to oxygen and UV-light for 190 hours, producing an approximately C60O1 stoichiometry in the bulk of the sample. C K-edge and O K-edge NEXAFS (using total fluorescence yield detection) and resonant
X-ray inelastic scattering (RIXS) spectra from the sample film were measured and the C K-edge data were compared to the spectra
from pristine C60 as reference. The C K-edge absorption and emission spectral profiles of the oxygen-doped sample are similar to those of the
C60 reference, suggesting that cage breaking of C60 under these conditions, if any, is negligible. However, the redistribution of intensities in the spectra indicates changes
in the occupancies of different molecular orbitals, possibly due to changes in electron density upon reaction. Similarities
of the O K-edge soft X-ray emission (SXES) spectra to several small oxygen-containing molecules is being discussed in terms
of bonding models.
Received 4 December 2000 相似文献
9.
J. Dabrowski J. Rożynek G.S. Anagnostatos 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):125-131
It is shown that among four models of the Nijmegen baryon-baryon interaction only model F --which leads to a repulsive potential
felt by the Σ hyperon inside the nucleus-- is consistent both with the analysis of Σ- atoms and of the (K
-,π) reactions. The Nijmegen models are used to determine the strong complex single-particle (s.p.) potential of Σ-, and to calculate the strong-interaction shifts and widths of the lowest observed levels of Σ- atoms. The results obtained with model F are in best agreement with the experimental data.
Received: 15 January 2002 / Accepted: 14 March 2002 相似文献
10.
A.V. Papoyan M. Auzinsh K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):63-71
We report results of a theoretical and experimental study of the ground state nonlinear Hanle effect under strong laser excitation.
It is shown that besides the well-known zero-magnetic field suppression of absorption on F
g = F→F
e = F - 1 transitions caused by population trapping, an optical pumping induced enhanced absorption occurs on F
g = F→F
e = F + 1 transitions for small B-fields. The latter effect becomes more pronounced for high F values. The experiment with atomic vapor of Cs (D2 line, F
g = 4) confirms an increase of the spectrally unresolved fluorescence yield at zero magnetic field and 600 mW/cm2 laser intensity by 9% or 42%, when excitation occurs with linearly or circularly polarized light, respectively. The results
of the experiment agree with numerical simulation studies using equations of motion for a density matrix.
Received 24 November 2001 / Received in final form 25 March 2002 Published online 24 September 2002 相似文献
11.
Ngai KL 《The European physical journal. E, Soft matter》2002,8(2):225-235
Large increases of mobility of local segmental relaxation observed in polymer films as the film thickness is decreased, as
evidenced by decreases of the glass temperature, are not found for relaxation mechanisms that have longer length scales including
the Rouse relaxation modes and the diffusion of entire polymer chains. We show that the coupling model predictions, when extended
to consider polymer thin films, are consistent with a large increase of the mobility of the local segmental motions and the
lack of such a change for the Rouse modes and the diffusion of entire polymer chains. There are two effects that can reduce
the coupling parameter of the local segmental relaxation in thin films. One is the chain orientation that is induced parallel
to the surface when the film thickness h becomes smaller than the end-to-end distance of the chains and the other is a finite-size effect when h is no longer large compared to the cooperative length scale. Extremely thin ( ≈ 1.5 nm) films obtained by intercalating a
polymer into layered silicates have thickness significantly less than the cooperative length scale near the bulk polymer glass
transition temperature. As a result, the coupling parameter of the local segmental relaxation in such thin films is reduced
almost to zero. With this plausible assumption, we show the coupling model can explain quantitatively the large decrease of
the local segmental relaxation time found experimentally.
Received 1 August 2001 and Received in final form 1 December 2001 相似文献
12.
C. Caraby L. Adoui J.P. Grandin A. Cassimi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):53-56
We report the observation of resonances in the intensity correlation spectra of a 3D rubidium optical lattice, which we attribute
to light scattering from propagating atomic density fluctuations in the lattice. This process is the spontaneous analog of
the stimulated scattering mechanism recently described by Courtois et al.. We investigate the dependence of the new resonances on the lattice angle and show that they disappear for large angles,
thus resolving previous discrepancies on the subject.
Received: 30 January 1997 / Accepted: 9 October 1997 相似文献
13.
P. Domokos T. Kiss J. Janszky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):49-53
A beam of diatomic molecules scattered off a standing wave laser mode splits according to the rovibrational quantum state
of the molecules. Our numerical calculation shows that single state resolution can be achieved by properly tuned, monochromatic
light. The proposed scheme allows for selecting non-vibrating and non-rotating molecules from a thermal beam, implementing
a laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble.
Received 23 August 2000 and Received in final form 17 November 2000 相似文献
14.
M. Abbate J.A. Guevara S.L. Cuffini Y.P. Mascarenhas E. Morikawa 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):203-208
We studied the changes in the electronic structure of SrTi1-xRuxO3 across the metal-insulator transition. The parent compound, SrTiO3, is a well known diamagnetic insulator; whereas the doped compound, SrTi1-xRuxO3, becomes a ferromagnetic metal above x
C
= 0.35. The techniques used in the study were photoemission (PES) and O 1
s X-ray absorption (XAS) spectroscopy. The experimental spectra were analyzed in terms of band structure and Hubbard model
calculations. The PES and XAS spectra of SrTi1-xRuxO3 show the Ru 4
d bands growing in the band gap of SrTiO3 . The analysis in terms of the Hubbard model indicates that the Ti 3
d and Ru 4
d bands are mostly decoupled. This suggests that the metal-insulator transition is a percolation transition like that of metals
embedded in a rare gas matrix. Electron correlation effects are present in this system, but they do not seem to play a major
role in the transition.
Received 10 September 2001 相似文献
15.
We calculate the decay of pionium atoms into two photons. The pion polarizabilities give rise to a 10% correction to the corresponding
decay width for pointlike pions. This opens the possibility to obtain the difference between the electric and magnetic polarizability
of the charged pion from a future measurement of the branching fraction of pionium into two photons. For such an experiment
the ππ-scattering lengths would have to be known to better than 5% precision. We also comment on the contribution of the axial
anomaly to the decay of pionium into γπ0.
Received: 1 March 1999 / Revised version: 31 May 1999 相似文献
16.
F. Arias de Saavedra E. Buendıa F.J. Gálvez A. Sarsa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):201-206
A generalized Hylleraas-type basis set with three nonlinear parameters is proposed to study three-body systems interacting
via coulomb forces within the framework of non-relativistic quantum mechanics. This basis set improves the rate of convergence
with respect to previous ones, specially for non-symmetric systems and excited states of two electron atoms. Accurate binding
energies and other properties for S-states of helium-like ions, muonic molecules and the positronium negative ion are reported.
Received 21 July 2000 and Received in final form 4 October 2000 相似文献
17.
Z. Ficek J. Seke A.V. Soldatov G. Adam N.N. Bogolubov Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):411-419
We investigate the absorption and dispersion properties of a two-level atom driven by a polychromatic field. The driving field
is composed of a strong resonant (carrier) frequency component and a large number of symmetrically detuned sideband fields
(modulators). A rapid increase in the absorption at the central frequency and the collapse of the response of the system from
multiple frequencies to a single frequency are predicted to occur when the Rabi frequency of the modulating fields is equal
to the Rabi frequency of the carrier field. These are manifestations of the undressing or a disentanglement of the atomic
and driving field states, that leads to a collapse of the atom to its ground state. Our calculation permits consideration
of the question of the undressing of the driven atom by a multiple-modulated field and the predicted spectra offer a method
of observing undressing. Moreover, we find that the absorption and dispersion spectra split into multiplets whose structures
depend on the Rabi frequency of the modulating fields. The spectral features can jump between different resonance frequencies
by changing the Rabi frequency of the modulating fields or their initial phases, which can have potential applications as
a quantum frequency filter.
Received 23 October 2001 and Received in final form 31 January 2002 相似文献
18.
M. Takigawa M. Ichioka K. Machida 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):303-311
Thermal conductivity κ
xx(T) under a field is investigated in d
x2 - y2-wave superconductors and isotropic s-wave superconductors by the linear response theory, using a microscopic wave function of the vortex lattice states. To study
the origin of the different field dependence of κxx(T) between higher and lower temperature regions, we analyze the spatially-resolved thermal conductivity around a vortex at
each temperature, which is related to the spectrum of the local density of states. We also discuss the electric conductivity
in the same formulation for a comparison.
Received 8 December 2001 and Received in final form 20 March 2002 Published online 6 June 2002 相似文献
19.
A. Benfredj D. Gamra S. Romdhane T. Barhoumi C. Guthmann J.L. Monge H. Bouchriha 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):385-391
The effect of a magnetic field (6 kG) on the delayed fluorescence in a 1,4-Dibromonaphtalene at 300 K and 20 K is analysed
using a new approach of calculation of the triplet-triplet annihilation rate constant. The agreement of the best fit between
experiment and theory allows reaching at 300 K and 20 K respectively the lifetimes and the interaction constant of the triplets
pairs.
Received 12 March 1999 and Received in final form 27 April 2000 相似文献
20.
T.S. Jensen V.E. Markushin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):261-270
The deexcitation of exotic hydrogen atoms in highly excited states in collisions with hydrogen molecules has been studied
using the classical-trajectory Monte Carlo method. The Coulomb transitions with large change of principal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n. The molecular structure of the hydrogen target is shown to be essential for the dominance of transitions with large Δn. The external Auger effect has been studied in the eikonal approximation. The resulting partial wave cross-sections are consistent
with unitarity and provide a more reliable input for cascade calculations than the previously used Born approximation.
Received 28 May 2002 Published online 15 October 2002
RID="a"
ID="a"e-mail: thomas@physik.unizh.ch 相似文献