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1.
duration ranging from femtoseconds to nanoseconds has been simulated. The effect of the absorption from excited singlet and triplet states on the transmissivity of the medium under two-photon excitation has been investigated. It has been shown that in a medium excited by monopulses, the S 1S n and T 1T m absorption makes a considerable contribution to the total nonlinear absorption of the medium only for nanosecond pulse durations. When a medium is excited by a sequence of femtosecond pulses with a repetition frequency of some tens of megahertz, significant additional nonlinear absorption can arise only due to T 1T m transitions that occur due to accumulation of molecules in triplet states. This effect should be taken into account in determining the cross-section for two-photon absorption in dyes and also in developing radiation intensity limiters for femtosecond lasers.  相似文献   

2.
We have studied the temperature dependence of the radiative deactivation of the Pd-porphine triplet states in Shpol’skii matrices in the temperature range 1.2–210 K. A substantial transformation of the phosphorescence spectra is observed as the temperature increases and is due to the inclusion of thermally activated Pd-porphine states in the radiative deactivation processes. The activation energy Ea of these Pd-porphine states is measured in matrices of n-octane and n-nonane. The splitting of the lowest quasidegenerate triplet state ΔE(T2−T1) is determined for planar and distorted conformations of the Pd-porphine macrocycle in the n-octane matrix as 40 and 57 cm−1, respectively. The ability to use the temperature dependence of the phosphorescence properties of Pd-porphine to fabricate molecular thermometers for the low-temperature range is analyzed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 460–464, July–August, 2007.  相似文献   

3.
The prospects of utilizing the strangeness production reaction γdK + Λn for the determination of the Λn low-energy scattering parameters are investigated. The spin observables that need to be measured in order to isolate the Λn singlet (1 S 0) and triplet (3 S 1) states are identified. Possible kinematical regions where the extraction of the Λn scattering lengths might be feasible are discussed.  相似文献   

4.
We study the energy current in a model of heat conduction, first considered in detail by Casher and Lebowitz. The model consists of a one-dimensional disordered harmonic chain of n i.i.d. random masses, connected to their nearest neighbors via identical springs, and coupled at the boundaries to Langevin heat baths, with respective temperatures T 1 and T n . Let E J n be the steady-state energy current across the chain, averaged over the masses. We prove that E J n ~ (T 1T n )n −3/2 in the limit n → ∞, as has been conjectured by various authors over the time. The proof relies on a new explicit representation for the elements of the product of associated transfer matrices.  相似文献   

5.
We have used quantum chemical methods for a theoretical study of the luminescent characteristics (including estimating the rate constants for intramolecular T1 → S0 electronic transitions) of the molecules of four immunoactive compounds of the 8-azasteroid class. We have established that the T1 state is localized on the enaminodicarbonyl moiety that is common to all the molecules. We have shown that for the studied compounds, the phosphorescence spectra and the physical mechanisms for deactivation of the lower triplet state T1 are similar. For all the compounds, the results of the theoretical study are consistent with the corresponding conclusions of experimental studies of 8-azasteroids. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 751–755, November–December, 2006.  相似文献   

6.
The fluorescence and triplet state quenching of 7-amino-1,3-naphthalenesulfonic acid by paramagnetic metal ions have been investigated in an aqueous medium. The basic mechanism of the fluorescence quenching involves the static and dynamic electron transfer to the paramagnetic cation. The induced S1→T1 intersystem crossing at fluorescence quenching of the fluorophore by Cu2+ cation has been found. There is a correlation between triplet state quenching rate constants and values of the efficient paramagnetic susceptibility and spin of the cations. The rate constants for the quenching pathways have been calculated.  相似文献   

7.
The effect of atomic disorder on the electron transport and the magnetoresistance (MR) of Co2CrAl Heusler alloy (HA) films has been investigated. We show that Co2CrAl films with L21 order exhibit a negative value for the temperature coefficient of resistivity (TCR) in a temperature range of 10 < T < 290 K, and the temperature dependence of electric conductivity varies as T 3/2 similarly to that of the zero-gap semiconductors. The atomic or the site disorder on the way of L21 → B2 → A2 → amorphous state in Co2CrAl HA films causes the deviation from this dependence: reduction in the absolute value of TCR as well as decrease in the resistivity down to ϱ(T = 293 K) ∼ 200 μΩ cm in comparison to ϱ(T = 293 K) ∼ 230 μΩ cm typical for the Co2CrAl films with L21 order. The magnetic-field dependence of MR of the Co2CrAl films with L21 order is determined by two competing contributions: a positive Lorentz scattering and a negative s-d scattering. The atomic disorder in Co2CrAl films drastically changes MR behavior due to its strong influence on the magnetic properties.  相似文献   

8.
A differential thermal analysis ΔT y (T) in vacuum has been performed, and the temperature gradient ΔT x (T) along the Ag2Se sample during the transition α → β has been studied. It has been shown that the transitions α → α′ and β′ → β are displacive transitions and that the transition α′ → β′ is a reconstructive transition. It has been found that the temperature gradient along the sample during the transition α′ → β′ passes through a deep minimum due to a strong increase in the specific heat capacity.  相似文献   

9.
0 –S1–Sm–Sn multilevel system. An Sm→S1 absorption recovery time of τS1 A=(600±100) fs is determined. The picosecond and femtosecond pulse excitation leads to S0→S1 ground-state absorption bleaching and S1→Sm first excited-state absorption bleaching. The excited-state absorption cross-sections σS1 ex(S1→Sm) and σSm ex(Sm→Sn) are determined. Received: 3 June 1996  相似文献   

10.
By the delayed fluorescence activated by direct multiphoton excitation of triplet molecules by CO2–laser radiation we have studied the prevailing deactivation pathways of triplet molecules with a high store of vibrational energy E vib. The dependences of the kinetic characteristics of delayed fluorescence on the presence of vapors and foreign gases have been used to estimate the rates and efficiencies of intermolecular vibrational relaxation in the vibrational quasi–continuum of the triplet state T 1. By the changes in the intensities and decay rates over a wide range of vibrational energies we have established the E vib dependences of reversible intercombination conversion between the states T 1 and S 1 and interconversion from T 1 to the ground electronic state S 0 for both the case of isolated excited molecules and at a steady vibrational temperature. It is shown that at high vibrational temperatures the radiationless transition from the T 1 state to S 0 has an activation character and is accomplished through the energy barrier. The conditions for going to an exponential dependence have been determined. It has been found that the obtained dependences are in good agreement with the known experimental results. The influence of molecular and environmental characteristics on the decay rate of triplet molecules is compared.  相似文献   

11.
In the nonadiabatic approximation, we study how intramolecular interactions affect the nonradiative energy degradation T 1 s S 0 of triplet sublevels s of the lowest triplet state of the dibenzo-p-dioxin molecule. We consider the role played in the degradation by the shape of promoting high- and low-frequency vibrational modes and by spin-orbit interactions separately in the carbon backbone of the molecule and in heteroatoms (oxygen). We find that σ-electrons of oxygen that correspond to the lone pair and to valence electrons play different roles in the nonadiabatic interaction.  相似文献   

12.
In the framework of the spectral integral equation, we consider the states and their radiative transitions. We reconstruct the interaction on the basis of data for the levels of the bottomonium states with J PC = 0−+, 1−−, 0++, 1++, 2++ as well as the data for the radiative transitions γ (3S) → γχbJ(2P) and γ(2S) → γχbJ(1P) with J = 0, 1, 2. We calculate bottomonium levels with the radial quantum numbers n ≤ 6, their wave functions, and corresponding radiative transitions. The ratios Br[χbJ(2P) → γγ(2S)]/Br[χbJ(2P) → γγ(1S)] for J = 0, 1, 2 are found to be in agreement with data. We determine the component of the photon wave function using the data for the e + e annihilation, e + e → γ(9460), γ(10 023), γ(10 036), γ(10 580), γ(10 865), γ(11 019), and predict partial widths of the two-photon decays ηb0 → γγ, χb0 → γγ, χb2 → γγ for the radial excitation states below the threshold (n ≤ 3). The text was submitted by the authors in English.  相似文献   

13.
The spectral-luminescent properties and electronic-level structure of a derivative of oxotetrahydrobenzo[c]phenanthridine—3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-one (DTP)—in polar and nonpolar solutions are studied by the luminescence and picosecond spectroscopy techniques at 293 and 77 K. It is shown that DTP exhibits ππp* fluorescence only in polar proton-containing methanol, ethanol, and n-propanol and that this fluorescence is associated with a chromophore + alcohol complex. Solutions of DTP in n-propanol and the nonpolar mixture methylcyclohexane + toluene (6:1) at 77 K display ππp* phosphorescence with a quantum yield ΦPh=0.1, a lifetime τPh=1.9 s, and a frequency of the 0-0 transition equal to 21550 cm−1. The fact that DTP fluorescence is absent in aprotic solvents and exists in alcohols is explained by the inversion of the energy levels of the S ππ* and T n π* states, as a result of which the energy level of the fluorescing S ππ* state in alcohol becomes the lowest. The picosecond spectra and kinetics of the inducedS n (ππ*) ← S 1(π π*) and T k (ππ*) ← T 1(ππ*) absorption made it possible to estimate the lifetime of the S 1(ππ*) state of DTP in n-propanol at 293 K (20±10 ps) and the position of the triplet-triplet absorption peak (495 nm). __________ Translated from Optika i Spektroskopiya, Vol. 94, No. 6, 2003, pp. 993–998. Original Russian Text Copyright ? 2003 by Bondarev, Knyukshto, Tikhomirov, Pyrko.  相似文献   

14.
High triplet quantum yields of more than 90% for bithiophene and terthiophene have to be connected with very fast and effective formation of triplets after excitation. We studied these processes with fs pump–probe spectroscopy. The time behaviour of transient optical spectra within the singlet and triplet manifold was examined for bi- and terthiophene (2T and 3T) in solution. For 2T we used two-photon absorption for excitation. We found transient spectra of the excited singlet state, the triplet state and that of radical cations. The kinetics of the excited-state absorption was described by a bi-exponential function. Additionally we observed formation and recombination of radical cations. The recombination is connected with triplet formation. Both processes could be described by a time constant of 62 ps±9 ps. For 3T we found a dependence of the processes on excitation energy using one-photon absorption. The triplet quantum yield increased with higher excitation energy. The kinetics becomes bi-exponential with increasing amplitude of the short time constant of 2 ps at increasing excitation energy. The main reasons for the effective intersystem crossing (ISC) in both oligothiophenes are – besides the high spin-orbit coupling factor introduced by the sulphur atom – the almost isoenergetic positions of the S 1 and T 2 states, detected by PD-PES [1]. At higher photon excitation energy for 3T above the band gap an additional channel for ISC was detected. We believe that during the geometric change from the non-relaxed non-planar to the relaxed planar excited state S 1, ultrafast intersystem crossing takes place. Received: 6 December 1999 / Published online: 2 August 2000  相似文献   

15.
Resonant absorption of microwaves in CuGeO3 single crystals in a frequency band of 40 to 120 GHz, in magnetic field B⩽15 T, at temperatures ranging between 0.5 and 300 K, and in the configuration Ba has been investigated. Several absorption lines (S 0, S a, and S b) whose parameters strongly depend on temperature have been detected close to ESR. The temperature dependence of the total absorption in the main line S 0 with the Landé g-factor g 0=2.154 at temperatures above the spin-Peierls transition temperature is in good agreement with Bonner and Fisher’s theoretical prediction for a one-dimensional Heisenberg spin chain. In addition to the main resonance, a resonance of smaller amplitude, S a, with the g-factor g a=2.72 has been detected at temperatures ranging down to a characteristic temperature T≃1 K, below which the amplitude of this feature drops to zero. A radical restructuring of the magnetoabsorption spectrum occurs at the temperature of the spin-Peierls transition T SP≈14 K. At T<12 K new features emerge in the spectrum, namely, a broad absorption line overlapping with the narrow lines S 0 and S a, and a line S b with g b=1.83, which is not detected at temperatures above T SP. An analysis of amplitudes and total absorption of ESR lines as functions of temperature has shown that the temperature range below 1 K is anomalous, which may be caused by an additional ordering in the CuGeO3 magnetic subsystem at low temperatures. Zh. éksp. Teor. Fiz. 112, 1727–1738 (November 1997)  相似文献   

16.
The quantum yield of2F5/22F7/2 luminescence of the Yb3+ ion has been measured for ytterbium tris-thenoyltrifluoroacetonate upon excitation in the UV S0 → S1 absorption band of a ligand and in the IR2F7/22F5/2 absorption band of the Yb3+ ion. It has been established that the quantum efficiency of intramolecular transfer of electron excitation energy from the lowest triplet state of the ligand to the excited2F5/2 level of Yb3+ is equal to unity. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 539–542, July–August, 2000.  相似文献   

17.
We prove additivity of the minimal conditional entropy associated with a quantum channel Φ, represented by a completely positive (CP), trace-preserving map, when the infimum of S12) − S1) is restricted to states of the form . We show that this follows from multiplicativity of the completely bounded norm of Φ considered as a map from L 1L p for L p spaces defined by the Schatten p-norm on matrices, and give another proof based on entropy inequalities. Several related multiplicativity results are discussed and proved. In particular, we show that both the usual L 1L p norm of a CP map and the corresponding completely bounded norm are achieved for positive semi-definite matrices. Physical interpretations are considered, and a new proof of strong subadditivity is presented.  相似文献   

18.
N Nambudripad  S K Dhar 《Pramana》1987,29(4):L433-L435
We have measured the heat capacity of superconducting, single phase YBa2Cu3O7 in the temperature range 2 to 18 K. An extrapolation of the data between 4 and 9 K gives aC/T (T → 0) of ∼ 25 mJ/mole K2. The Debye temperature obtained from the high temperature linear portion ofC/T vsT 2 plot is 325 K.  相似文献   

19.
Based on studies of spectral and kinetic parameters of dimers of Zn porphyrins and of multiporphyrin self-assembling complexes formed on their basis, we find that extra liganding of dimers by pyridine inappreciably lowers the energy of the triplet level E(T 1). We show that, in this case, the nonradiative deactivation T 1S 0 of the electronic excitation energy of dimers Zn porphyrins increases not only due to increasing Franck-Condon factor. We discuss mechanisms of the quenching action of an extra ligand related to an accepting role played by high-frequency overtones of vibrations of extra ligand molecules, to an enhancement of the spin-orbit interaction due to energy lowering of σπ* states, and to out-of-plane distortion of dimers caused by the displacement of the Zn2+ ion out of the plane of the tetrapyrrole macrocycle. Quenching of triplet states of extra liganded dimers of Zn porphyrins by molecular oxygen in liquid solutions at 295 K depends on the character of donor-acceptor interactions with pyridine and rigidity of a linking molecular fragment. We find that the rate constants of oxygen quenching of the excited electronic states S 1 and T 1 of multiporphyrin complexes depend on their structure and composition, as well as steric hindrances, created by dimers (screening effects) for contact interactions of a π-conjugated system of the free base (extra ligand) with molecular oxygen. Screening effects of extra ligands by dimer molecules of Zn porphyrins, which reduce the oxygen quenching rate constants k S and k T , are found to barely affect the singlet-oxygen generation quantum yield γΔ.  相似文献   

20.
The correlations of the linear and circular polarizations in the system of two photons have been theoretically investigated. The polarization of a two-photon state is described by the one-photon Stokes parameters and by the components of the correlation “tensor” in the Stokes space. It is shown that in the case of two-photon decays π0 → 2γ, η → 2γ, K L 0 → 2γ, K S 0 → 2γ and the cascade process |0〉 → |1〉 + γ → |0〉 + 2γ(|0〉 and |1〉 are states with the spin 0 and 1, respectively) the final two-photon state represents a characteristic example of the entangled (nonfactorizable) state, and the correlations between the Stokes parameters in all these decays have the purely quantum character: the incoherence inequalities of the Bell type for the components of the correlation “tensor”, established previously for the case of classical “mixtures”, are violated. The general analysis of the registration procedure for two correlated photons by two one-photon detectors is performed.  相似文献   

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