共查询到20条相似文献,搜索用时 31 毫秒
1.
A. M. Bonch-Bruevich E. N. Kaliteevskaya T. K. Razumova A. D. Roshal’ A. N. Tarnovskii 《Optics and Spectroscopy》2000,89(2):216-224
The localization of molecular orbitals in 2,4,6-substituted derivatives of pyrylium is studied. The conformation of three asymmetrical molecules with oxyethyl substituents in positions 2 and 4 and different substituents in position 6 of the pyrylium ring is calculated by the AM1 method. The localization of the four upper occupied and two lower unoccupied MOs is determined, the fragment localization numbers are found, and the energies of five optical transitions, localization numbers, and the numbers of charge transfer between fragments are calculated. The conformation analysis of molecules in the S 0 and S 1 states is performed. Solid and liquid pyrylium solutions of different viscosity and polarity are experimentally investigated. The absorption spectra are recorded and absorption cross sections are measured, as well as fluorescence spectra and fluorescence anisotropy spectra. The following conclusions are made. In nonplanar molecules of pyrylium salts, four absorption transitions are localized at different parts of the molecule containing the pyrylium ring and one of the substituents. Upon excitation of molecules with complex substituents in position 6, the molecular fragment in position 2 turns around. This results in a flattening of the molecular fragment containing the pyrylium ring and substituents 2 and 6 on which the fluorescence transition is localized. The rearrangement involves the lowamplitude motion; it occurs almost without a loss of the excitation energy and only slightly affects the localization of molecular orbitals. As a result, two excited conformers are formed that possess close absorption and fluorescence properties. The radiative transitions in these conformers completely determine fluorescence of liquid solutions of any viscosity, including glycerol solutions. Strong solvatochromism is related to the nonplanar structure of stable pyrylium molecules, whereas the weak solvatochromism of liquid solutions is caused by localization of radiative transitions on a planar fragment of unstable fluorescing conformers. 相似文献
2.
Shammai Speiser 《Czechoslovak Journal of Physics》1998,48(4):495-506
Intramolecular electronic energy transfer (intra-EET) was investigated in an isolated bichromophoric naphthalene (N) and anthracene
(A) 1:1 molecular cluster. Investigation of the spectroscopic properties of these chromophores, separately and loosely bound
in a van der Waals complex, helps to understand the dependence of the EET rate on the initially excited vibronic level and
on the cluster’s interchromophoric orientation. A slow intra-EET rate that is associated with an unfavoured orientation of
the two chromophores in one of the two possible conformers of the A-N cluster, was observed and was supported by a calculation
of the cluster geometry and by comparison with a recent study of intra-EET in the A-(CH2)n-N bichromophoric molecules.
Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic,
26–30 May 1997.
This study was partially supported by grants from the VPR Technion — N. Haar and R. Zinn Research Fund and by the Fund for
the Promotion of Research at the Technion. 相似文献
3.
I. V. Sokolova N. Yu. Vasil'eva Ya. O. Vylegzhanina G. V. Maier 《Russian Physics Journal》1993,36(9):882-886
Quantum-chemical calculations of trans-stilbene and benzene molecules as well as molecules of bifluorophores based on them — trans-stilbene-CH2-coumarine 120 and phenyl-CH2-coumarine — were performed by the INDO/S method. The form of the molecular orbitals, the distribution of the electron density in the ground and excited states, the spectra and nature of the electronically states of bifluorophore molecules were established in relation to the energy donor and acceptor molecules. Three conformations of the bifluorophore molecules were studied (planar, edge, wing). It was discovered that the energy and type of the molecular orbitals of the bifluorophores are independent of the relative orientation of the donor and acceptor subsystems. It is shown that the mixed character of the three lowest electronically excited states, participating in the formation of the spectrum, of the bifluorophores gives rise to quite appreciable overlapping of their electronic wave functions and, therefore, ensures that the internal-conversion processes are efficient.V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 83–88, Septmeber, 1993. 相似文献
4.
R. Thissen P. Lablanquie R.I. Hall M. Ukai K. Ito 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):335-342
Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron
and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence
states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve
as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer,
the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the
class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that
loses its innershell electron to its neutral partner.
Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998 相似文献
5.
H. Ring R.T. Carter J.R. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):487-493
By means of quantum beat spectroscopy we investigated the dynamics of magnetic moments associated with hyperfine levels in
the molecule under “spin-flip conditions”. Oriented molecules in a cold beam were prepared by excitation with a circularly polarized laser
pulse () in a weak magnetic field (). Subsequently, they were exposed to a rapid field inversion which left the magnetic moment in its initial orientation. The
initially created coherences among the excited hf levels were conserved after field reversal and thus were explored to characterize
the changes in the level structure due to this “Majorana spin-flip” process.
Received: 4 February 1999 相似文献
6.
Yu. D. Lantukh S. N. Pashkevich S. N. Letuta E. K. Alidzhanov A. A. Kul’sarin 《Optics and Spectroscopy》2011,110(6):880-884
Using electronic absorption, luminescence, and vibrational spectroscopy, we study the properties of DNA-acridine orange biopolymer
films. The conformational structure of DNA molecules in the film is examined at different levels of the relative humidity,
and the state of dye molecules incorporated into the structure of the biopolymer is estimated. These structures were formed
according to the “guest-host” principle and the dye molecule acts as the “guest” and the “host” is the intercalative DNA binding
sites. In such system dye molecules demonstrate high luminescence capability and are the uniform optical centers and their
fluorescence spectrum doesn’t depend on excitation wavelength. 相似文献
7.
M. V. Krasin’kova 《Technical Physics》1998,43(11):1347-1349
The question of the dimensionality of superconductivity is considered within the framework of a model of superconductivity
via asymmetric, delocalized “crystalline” π orbitals (analogous to the corresponding molecular orbitals) extending along chains of covalently bonded copper and oxygen
ions. It is shown that superconductivity is preceded by a separation of the bonds in the CuO2 layer into covalent and ionic bonds with ordering of the covalent bonds into chains. Such an ordering facilitates the formation
of a crystalline π orbital lowering the crystal energy by the resonance energy of the π bond and is therefore favored. The superconducting current is created by non-dissipative motion of π-electron pairs along the asymmetric, “crystalline” π orbitals extending along chains of covalently bonded copper and oxygen ions, in the presence of an ionic bond between neighboring
chains extending through the easily polarizable O2− ions. This ionic bond correlates the motion of the electron pairs along all the π orbitals and stabilizes the superconducting state. Only in this sense is the apparent “onedimensionality” of superconductivity
in cuprate superconductors to be understood.
Zh. Tekh. Fiz. 68, 82–84 (November 1998) 相似文献
8.
M. Glasbeek 《Czechoslovak Journal of Physics》1998,48(4):417-422
Time-resolved fluorescence up-conversion experiments have been performed for a few fluorescent organic charge transfer molecules
in liquid solution. Dynamic Stokes shifts have been measured, with a time resolution of 150 fs, for the probe molecules in
alcoholic and ethereal solvents. The results reveal solvation dynamics determined by “inertial free streaming” motions of
the solvent molecules in the solvent cages and rotational diffusion motions of the solvent molecules. Simulations of the temporal
changes in the fluorescence spectra based on the Smoluchowski diffusion equation are also briefly discussed.
Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic,
26–30 May 1997.
This work was supported in part by the Netherlands Foundation for Chemical Research (SON) with financial aid from the Netherlands
Organization for Scientific Research (NWO). 相似文献
9.
M. P. Samtsov S. A. Tikhomirov O. V. Buganov K. N Kaplevsky D. G. Melnikov L. S. Lyashenko 《Journal of Applied Spectroscopy》2009,76(6):783-790
Spectral-kinetic and photochemical properties of HITC dye with iodide and perchlorate counterions have been studied in environments
where the dye molecules exist in different ionic forms. In ethanol, the dye molecules exist as free ions; in dichlorobenzene,
as contact ion pairs. Superfast transformation of non-stationary spectra in an HITC dye bleaching band is found. The observed
effects are interpreted within the framework of concepts on “burning out” a notch in the contour of a non-uniformly widened
vibronic band of S
0 → S
1-absorption. Qualitative differences in recorded absorption spectra from the dye excited electronic states for weakly and
highly polar solvents are found. It is shown that the observed differences are caused by superfast charge transfer in the
contact ion pairs that results in the formation of free radicals. 相似文献
10.
G. P. Miroshnichenko 《Journal of Experimental and Theoretical Physics》2009,109(2):193-206
A theory of the discrete photodetection of quantum jumps on the V configuration of atomic levels has been developed. A three-level
source atom is placed in a cavity excited by a resonance fluorescence field. The cavity is tuned to exact resonance with an
atomic transition. The cavity mode state is tested by a flux of unexcited (at the entrance) probe atoms passing through the
cavity. The energy states of the outgoing probe atoms are detected by ionization chambers, which are assumed ideal. This a
posteriori statistical information is indirectly related to the numerical characteristics of a measured quantum system consisting
of the source atom and cavity mode. The “tuning” conditions for a discrete photodetector, i.e., the rules for choosing the
parameters and durations of the interactions of the cavity mode with the probe and source atoms, intensities of the pump and
probe fields that are necessary for observing quantum jumps from the “bright” state to the “dark” one and vice versa, have
been determined. A two-state model that describes the dynamics of a quantum jump has been analyzed. The formulas have been
obtained for the observable characteristics of quantum jumps: the mean residence time of the quantum system in quasistationary
states (durations of the bright and dark periods), probabilities of quantum jumps, mean excitation levels of the quantized
cavity mode, etc. 相似文献
11.
V. Bonačić-Koutecký J. Pittner D. Reichardt P. Fantucci J. Koutecký 《Czechoslovak Journal of Physics》1998,48(6-7):637-658
The aim of this contribution is to show that quantum chemistry has suitable tools to extract the specific properties of small
metallic and mixed non-stoichiometric clusters which cannot be obtained by extrapolation from the bulk properties to the atom.
For this purpose, first the main features of the methods used for the calculations of the ground and excited states of clusters
valid at zero temperature (T=0) will be sketched and the factors determining accuracy of results will be pointed out. The structural and optical response
properties of cationic Na
n
+
clusters as a function of size will be presented and compared with experimental data. The series of non-stoichiometric alkali-halide
clusters containing single and multiple excess electrons will serve as prototypes to study a possible “metal-insulator transition”
and “segregation into metallic and ionic parts” in finite systems. Second, an outline of ab initio molecular dynamics methods
based on gradient corrected density functional approach with gaussian basis used for determination of temperature dependent
ground state properties will be presented. Different temperature behavior of distinct type of structures will be illustrated
on an example of Li
9
+
cluster.
Presented by V. Bonačić-Koutecky at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September
1–5, 1997.
This work has been supported by the Deutsche Forschungsgemeinschaft (SFB 337, Energy transfer in molecular aggregates) and
the Consiglio Nationale delle Ricerche (CNR, Rome). 相似文献
12.
V. F. Gavrikov A. N. Dvoryankin A. A. Stepanov A. K. Shmelev V. A. Shcheglov 《Journal of Russian Laser Research》1994,15(3):177-212
We analyze the basic thermodynamic, kinetic, radiative, and spectroscopic properties of halogen and interhalogen molecules
which are potentially suitable for the construction of visible and near-IR chemical lasers. We discuss the problem of chemical
buildup of electronically excited states (EES) of donor molecules (or atoms). We propose a number of new kinetic schemes with
formation of EES of donor particles, for the development of lasers based on electronic transitions (ET). We obtain analytic
relations for the lasing condition and for the laser efficiency of a system of a “donor—acceptor” type as applied to ET chemical
lasers. Actual results of research into the gain properties and energy characteristics of potential visible-band chemical
NF-IF and N2-IF lasers. The possibility of using atoms in chemical lasers is discussed.
Translated from Trudy Fizicheskogo Instituta im. P. N. Lebedeva Akademiya Nauk SSSR, Vol. 194, pp. 171–211, 1989. 相似文献
13.
T. Ritschel P. J. Kuntz L. Zülicke 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):93-107
ArnHCl+ van-der-Waals clusters for n = 1–13 are investigated
with the “minimal diatomics-in-molecules (DIM) model”
using ab-initio input data obtained from multi-reference
configuration-interaction calculations plus subsequent projection onto
valence-bond wavefunctions.
The results for the complexes with n = 1–3 are checked against
ab-initio calculations at the
coupled-cluster (CCSD) level with the same one-electron atomic basis set as
for the input data generation (aug-cc-pVTZ from Dunning).
In addition to the electronic ground state,
the first excited
2A¢^2\!A^{\prime}
state for the triatomic
complex (n = 1) is also studied.
The results
from the DIM model are shown to be in fair agreement with those from
advanced conventional ab-initio calculations, although there are
differences in detail. The comparison
justifies the extension of the DIM approach to n > 3.
Systematic analysis of the local minima of the multi-dimensional
potential-energy surfaces (PESs), carried out with the combined
method
described in part I (Monte-Carlo sampling plus subsequent steepest-descent
optimization), reveals simple building-up regularities for the most
stable structures (i.e. those corresponding to the global PES minimum)
at each n: apart from always having a nearly linear
(Ar–H–Cl)+ fragment as core, the aggregates show little
or no symmetry. Secondary local minima are also determined and their
structures interpreted.
The PESs for the low-lying excited states reveal a much more complicated
topography compared to the ArnH+ clusters allowing a variety
of photo-processes.
The energy level sequence of the first five excited electronic states
and the stability of the clusters in these states is studied
as a function of the cluster size n. 相似文献
14.
T. Ritschel Ch. Zuhrt L. Zülicke P. J. Kuntz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):127-141
ArnHCl+ van-der-Waals clusters for n = 1–13 are investigated
with the “minimal diatomics-in-molecules (DIM) model”
using ab-initio input data obtained from multi-reference
configuration-interaction calculations plus subsequent projection onto
valence-bond wavefunctions.
The results for the complexes with n = 1–3 are checked against
ab-initio calculations at the
coupled-cluster (CCSD) level with the same one-electron atomic basis set as
for the input data generation (aug-cc-pVTZ from Dunning).
In addition to the electronic ground state,
the first excited
state for the triatomic
complex (n = 1) is also studied.
The results
from the DIM model are shown to be in fair agreement with those from
advanced conventional ab-initio calculations, although there are
differences in detail. The comparison
justifies the extension of the DIM approach to n > 3.
Systematic analysis of the local minima of the multi-dimensional
potential-energy surfaces (PESs), carried out with the combined
method
described in part I (Monte-Carlo sampling plus subsequent steepest-descent
optimization), reveals simple building-up regularities for the most
stable structures (i.e. those corresponding to the global PES minimum)
at each n: apart from always having a nearly linear
(Ar–H–Cl)+ fragment as core, the aggregates show little
or no symmetry. Secondary local minima are also determined and their
structures interpreted.
The PESs for the low-lying excited states reveal a much more complicated
topography compared to the ArnH+ clusters allowing a variety
of photo-processes.
The energy level sequence of the first five excited electronic states
and the stability of the clusters in these states is studied
as a function of the cluster size n. 相似文献
15.
16.
Electron attachment spectroscopy is employed to demonstrate that the scattering of slow (0–15 eV) electrons from perylenetetracarboxilic
dianhydride (PTCDA) molecules in the gas phase leads to the resonant formation of molecular and fragment negative ions detected
in the mass-spectrometric experiment. Depending on the electron energy, currents of anions have clearly manifested peaks at
0.14, 1.9, 3.0, 4.8, and 5.7 eV. In addition, resonant states are also detected at thermal energy (0 eV) of scattered electrons,
as well as at 0.4 and 1.0 eV, as shoulders on experimental curves. The spectroscopic states of PTCDA anions at energies exceeding
0 eV are interpreted in terms of the formation of shape resonances on the basis of calculated values of energies of π*-type
unoccupied molecular orbitals. It is found that the positions of unoccupied orbitals of an isolated PTCDA molecule correspond
to the peaks in the density of states of the conduction band of PTCDA films provided that the energies of the orbitals are
shifted by 1.4 eV. The latter value can be interpreted as the binding energy of a molecule in the film due to the polarization
interaction with the surroundings. 相似文献
17.
A one-configuration approximation is used to analyze the possibility of employing the frozen ion core model to calculate excited states with low-lying configurations of the same symmetry when the wave functions of the excited states are orthogonal to the function of the ground state. The nonorthogonality of the wave functions of different excited configurations is then weak. A calculation is made for certain Isns1S and 1s22sns1S terms of two-and four-electron ions, respectively, and the relaxation effects in the core are investigated for these excited states. This approximation is employed to obtain a variational equation for virtual orbitals allowing for the core relaxation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 71–77, June, 1980. 相似文献
18.
V. N. Knyukshto É. I. Zen'kevich E. I. Sagun A. M. Shul'ga S. M. Bachilo 《Journal of Applied Spectroscopy》1999,66(4):588-592
It is shown that at 295 K in meso-orthonitrophenyl-substituted octaethylporphyrins and their chemical dimers the steric interactions
of the nitro-group and the volume substituents at β-positions of the pyrrole rings favor direct overlapping of molecular orbitals
in a donor-acceptor pair. The efficient quenching of fluorescence of the nitroporphyrins in toluene is attributed to direct
nonadiabatic electron transfer from the S1-level of a porphyrin to the lower-lying state with charge transfer by the “through-space” mechanism. Quenching of the T1-states is related with heat-stimulated transmission to the higher-lying states with charge transfer of the ion-radical pair
as well as with enhancement of the probability of the nonradiative T1→S0-transition.
To whom correspondence should be addressed.
Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 531–535, July–August, 1999. 相似文献
19.
A. D'Andrea D. Schiumarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):87-101
The optical properties of Bragg quantum wells are studied
for exciton confinement under center-of-mass quantization. A variational
model of Wannier exciton envelope function, that embodies the correct
boundary conditions for center-of-mass, is adopted for calculation. The
present non-adiabatic exciton model is compared with adiabatic results and
with heuristic “hard sphere” model. The radiative self-energy of a
single-quantum well (SQW) and multi-quantum wells (MQWs) are computed in the
semiclassical framework, and in effective mass approximation, by
self-consistent solution of Schroedinger and Maxwell equations. This
microscopic solution is free from “fitting” parameter values, except for
the non-radiative broadening, and also the exciton dead-layer and the
additional boundary condition are not taken ad hoc, but come coherently
from the variational principle and self-consistent Schroedinger-Maxwell
solution. Dispersion curves of exciton-polariton propagating in a MQW, under
Bragg condition, are studied by selected numerical examples. The case of
optical gap in correspondence of higher excited states is studied, and,
moreover, the interesting effect of gap enhancement or inhibition, in
correspondence of non-resonant Bragg energy, will be addressed. 相似文献
20.
We have shown that in slow thermal reactions of complex molecules, effects of nonradiative transitions due to quantum beats
between resonant states of the combining molecular structures can be observed in conventional (without high time resolution)
IR absorption spectra, as oscillations in the intensities of individual lines. We suggest a method to ensure the required
level of coherence for the oscillations in an ensemble of molecules, based on application of pulsed heating to the molecular
system. Detection of the qualitatively new effects by traditional IR spectroscopy methods, including their quantitative characteristics,
considerably increases the information content of the spectral data obtained and makes it possible to use such highly developed
experimental methods to study chemical reactions, including the reaction dynamics. The range of these reactions is quite broad,
encompassing both “laboratory” and “natural” (geochemistry, ecology, etc.) processes with characteristic times on the order
of minutes or more.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 738–743, November–December, 2007. 相似文献