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1.
At certain magnetic fields, when the energy separations between the τx — τy spin levels and between the τy — τz levels of triplet coumarin become equal, intensity changes are observed in the phosphorescence of coumarin doped in a single crystal of durence cooled to 1.6 K that can be attributed to cross relaxation (CR) between the τx — τy spin levels of one triplet coumarin molecule and the τy — τz spin levels of another triplet coumarin. Rate equations that describe the time behavior of the populations of the spin levels which are involved in the CR process are described and numerically solved. CR behavior is found to be strongly dependent on the total coumarin triplet concentration.  相似文献   

2.
《Chemical physics》1987,112(1):23-41
The general series expansion for the joint angular velocity-orientation conditional probability density for a fluid composed of asymmetric top molecules is derived, and expressions for the reorientational correlation functions, correlation times, spectral densities, and the correlation times relevant to magnetic relaxation via spin-rotation interactions are presented. The reorientational correlation times and spin-rotation functions computed using this Fokker-Planck-Langevin (FPL) model with isotropic friction tensor (τx = τy = τz) are compared with the corresponding times and functions computed with the J-diffusion limit of the extended diffusion (EDJ) model. The models are found to predict significantly different behaviour only in the regime where free rotation and precessional effects become important. The reorientation self- and cross-correlation times are shown to follow Hubbard relations in the limit of short τx, τy, τz. Numerical calculations of the FPL reorientational correlation functions, correlation times and spin-rotation functions show that these properties are sensitive to the anisotropies in the friction tensor in the rotational Langevin equation.  相似文献   

3.
The delayed coincidence photon counting technique, employing a picosecond tunable dye laser as an excitation source, has been used for accurate determinations of radiative lifetimes of excited states. Excitation from meta-stable states of sputtered atoms was employed. We obtained for Cu: τ(3d 10 4p 2 P 1/2 = 7.27(0.06) ns, τ(3d 10 4p 2 P 3/2) = 7.17(0.06) ns and for Fe: τ(3d 7 4p y 3 F 2)= 9.06(0.16) ns, τ(3d 7 4p y 3 F 3) = 9.06(0.13) ns and τ(3d 7 4p y 3 F 4) = 9.11 (0.16) ns. Also, the ability of this technique to record quantum beats at frequencies up to 1 GHz is demonstrated.  相似文献   

4.
β-Alanyl-ciliatine (β-Ala-Cilia) studied in the solid state by X-ray diffraction and IR spectrometry, is shown to exist as the monobydrated zwitterion H3N+CH2CH2CONHCH2CH2PO3H?, H2O. Its conformation in the crystal (P21/c space group, Z = 4) is defined by: τ1 = +66.1°, ψ = ?157.4°. φ = +140.3°, τ2 = +175.4°, τ3 = +50.0°, τ4 = +80.1° and is compared with those of similar molecules. A partial interpretation of the IR spectra is given. A conformational energy calculation of the isolated zwitterion shows different conformations stabilized by various types of chelation.  相似文献   

5.
Theory is developed and compared to experiment for the cyclic voltammetric ejection and redeposition of solvated electrons es? in NaClO4 and LiCl solutions in HMPA. In current reversal chronopotentiometry, es? mass transfer can be observed free from uncompensated resistance effects by cathodic generation of es? for time tf followed by anodic current redeposition leading to a reverse transition time τb. The ratio τb/tf depends on tf, applied current, and LiCl electrolyte concentration. Comparison of τb/tf to theory detects a highly reactive scavenger at micromolar concentration levels.  相似文献   

6.
The radiative lifetimes of the states in the (n=5–8) 3snp 1 P 1 sequence of neutral magnesium were investigated using time-resolved laser-induced fluorescence. Excitation from the 3s 2 1 S 0 ground state was performed using VUV radiation, which was produced by resonant sum-difference frequency mixing in a krypton gas cell. We find τ(n=5): 54(3) ns, τ(n=6): 140(10) ns, τ(n=7): 290(20) ns. τ(n=8): 475(40) ns. These results were found to be in fair agreement with a Multi Configuration Hartree-Fock (MCHF) calculation.  相似文献   

7.
《Chemical physics》1987,116(1):101-111
The 2D and 19F spin-lattice relaxation times of 1,3,5-trifluorobenzene-d3 in 0.15 mol fraction solutions in various solvents have been measured over the temperature range 270–400 K. The relationship between the reorientational correlation times, τθ, and the angular momentum correlation times, τJ, obtained from the nuclear relaxation data has been compared with the theoretical relationships predicted by the J-diffusion limit of the extended diffusion (EDJ) model and the Fokker-Planck-Langevin (FPL) model for symmetric top molecules. It was found that the rotational motion of 1,3,5-trifluorobenzene-d3 in most solutions was better described by the FPL model with frictional anisotropy τ6· in the range 1–2. (τ6 and τ· are the correlation times for the angular velocity components along the axes parallel and perpendicular to the molecular symmetry axis.) The viscosity and temperature dependence of τθ has been analyzed in terms of a modified Debye equation and values for the anisotropic interaction parameter, κ, in each solvent are reported. The variation in κ with solvent is attributed mainly to the variation in the dipole moment of the solvent molecules. The frictional anisotropy (τ6·) is found to decrease as κ increases. This is interpreted in terms of the effects of molecular shape and electrostatic interactions between CF bond dipole moment and solvent dipole moments.  相似文献   

8.
Bromine hyperfine and quadrupole fine structure has been observed in the 3 cm MODR spectrum of the photoexcited 3B1u state of symmetric tetrabromobenzene (s?TBB) in a durene host crystal at liquid helium temperature. A preliminary analysis of the observed structure yields the two in-plane values of the bromine hyperfine tensor |Ay/gβl = 10.3 and |Az/gβ| = 16.5 (for 81Br), and a comparison of these values with those recently observed for the α-bromomaleic acid radical suggests that the correct zero-field scheme in the lowest triplet state of s-TBB is τN > τM > τL.  相似文献   

9.
《Chemical physics》1987,115(1):15-21
Second-order polarization propagator calculations of the X1Σ+ → A1II transition moment as well as the radiative lifetime of the A1II state of BH are reported. The calculated vibrational lifetimes are τ(v′ = 0) = 121 ns, τ(v′ = 1) = 129 ns, and τ(v′ = 2) = 137 ns. The τ(v′ = 0 lifetime agrees with the most recent experiment of τ(v′ = 0) = 125 ± 5 ns. We show that the electronic oscillator strength computed at the ground state equilibrium is rather different from the band absorption oscillator strength f00, which demonstrates that theoretical electronic oscillator strengths should not be expected to agree with experimentally determined band oscillator strengths.  相似文献   

10.
Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d 3 D 1 0 )=0.209±0.007 ns, τ(2p 3d 3 D 2 0 )=0.219±0.007 ns, τ(2p 3d 3 D 3 0 )=0.217±0.005 ns, and τ(2p 3d 1 P 1 0 )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.  相似文献   

11.
We have measured radiative lifetimes for selenium and tellurium resonance levels by using short pulse laser excitation in differentially heated resonance cells. We obtained τ(3 S 1 Se I)=2.9(5) ns and τ(3 S 1 Te I)=3.1(5) ns, which together with branching ratio values given by Ubelis and Berzinsh yield the absorption oscillator strengthf abs(Se I, 196.0 nm)=0.074(16) andf abs(Te I, 214.3 nm)=0.098(17).  相似文献   

12.
Positron lifetime measurements were performed on eight different amino acids, τ1, τ2 and I2 values were observed at around 0.35 nsec, 0.7–1.2 nsec and 20–30%, respectively. The long-lived component seems to be produced by positronium states trapped in the crystalline lattice or by positronium atoms bound to molecules.  相似文献   

13.
Depolarized Rayleigh scattering spectra have been measured using a Fabry-Pérot interferometer for 1,3,4-[D2] thiadiazole at temperatures between 20 and 92.5°C, covering a large portion of the liquid and supercooled liquid regions. From the spectral halfwidth measurements, the Rayleigh relaxation times, τRay, have been obtained. A semilog plot of τRay versus T?1 shows that the data fit well to an Arrhenius equation, with activation energy equal to 2.4 kcal/mole. The relation of τRay to pair orientation correlations is discussed.  相似文献   

14.
Using picosecond spectroscopy, we find rise times τR ? 20 ps for p-dimethylaminobenzonitrile S2 → S0 fluorescence in the weakly hydrogen-bound alcohols 2,2,2-trifluoroethanol and 2-fluoroethanol. Since we previously obtained τR ≈ 40 ps in methanol and ethanol, this provides evidence that hydrogen-bonding-retarded solvent reorientation largely governs the fluorescence in these solvents.  相似文献   

15.
《Chemical physics》1986,108(3):373-379
The hydroxymethyl radical oxidation kinetics follows the second-order equation with a time-dependent rate constant, K(t). The annealing effect is described by way of dividing K(t) into two factors, one of them depending on the preliminary annealing time (τ): K(t) = K1(t + τ)K2(t). The time dependence of both factors is fairly well approximated by the power functions: K1(t + τ) ≈ (t + τ)−0.18 and K2(tt−0.26. The oxygen quenching of phenanthrene phosphorescence follows an exchange mechanism, with the static conditions setting in at 77 K. At 90 K oxygen diffusion adds to the quenching efficiency. The time of oxygen jumps (τj) and its time dependence under the matrix annealing at 90 K are determined by comparing the theoretical 1/τj dependence of the quenching volume with experiment. The 1/τj(τ) is well described by the power function τ−0.18 ± 0.02). The annealing time functions of the oxidation rate constant and of the inverse jumping time are similar. The oxidation rate constant and the diffusion constant coincide in the order of magnitude. Consequently, the slowing down of oxygen migration contributes essentially to the time dependence of the rate constant.  相似文献   

16.
The steady-state and time-resolved fluorescence spectra of complexes formed from α,β,γ,δ-tetrakis(4-carboxyphenyl) porphin and the synthetic sequential polytripeptides poly(L-lysyl-L-leucyl-L-alanine)n (I) (MW 7900) and poly(L-lysyl-L-alanyl-L-alanine) n (II) (MW 6900) are studied in phosphate buffer (pH=7.2). The peptide matrices were found to bond 4-5 pigment molecules per one polypeptide. The complexed pigment fluorescent decay kinetics is two-exponential with components τ1 =240 ps and τ2=2400 (I) and 3500 ps (II). The relative contributions of τ1 correlate with the degree of α-helicity of the polypeptide matrix.  相似文献   

17.
Radiative lifetimes were determined for two short-lived states in neutral nitrogen. Following photo-dissociation and two-photon excitation employing the same UV source, excitation to higher states was performed with a distributed feedback dye laser (DFDL). The lifetimes were found to be τ(2p 24d 4 D 7/2)=17(3) ns and τ(2p 25s 4 P 5/2)=22(3) ns.  相似文献   

18.
A dry resist-free process of electron-beam vapor deposition of an undecane precursor (C11H24) mask on SiO2-on-silicon and copper-on-silicon substrates was studied. The band section was trapezoidal, and the band width at the base was much larger than the diameter of the electron beam and depended on the substrate (it was three or four times larger on copper than on SiO2). In mask deposition on copper, the mask thickening rate v was found to depend strongly on the scan time τsc when scanning was performed along the band. When τsc changed from 20 ms to 13 s, v decreased by a factor of 7.4 (beam current 1.0 nA). This was probably caused by significant diffusion delay of precursor transport to the reaction zone during pixel time when τsc was 13 s. The ion-beam etching of the substrates through the deposited masks was performed (the SiO2 substrate was etched with SF6 ions, and the copper substrate, with Ar ions).  相似文献   

19.
Analytic expressions for dielectric permittivity factor ε1(ω) and dielectric dissipation factor ε2(ω) of electrolyte solutions are obtained, based on the ratio between complex factors of dielectric permittivity and specific conductivity. The range of frequency dispersion of dynamic factors ε1(ω) and ε2(ω) for aqueous solutions of LiCl, NaCl, KCl, and CsCl is considered. Numerical calculations are performed for friction coefficients β a and β b ; relaxation times τ a , τ b , and τ ab ; and factors ε1(ω) and ε2(ω) in a wide range of variation for ρ; concentration c; temperature T; and frequencies ω. The resulting theoretically calculated ε1(ω) and ε2(ω) values and the Cole–Cole diagram are in quantitative agreement with experimental data.  相似文献   

20.
The vs(XH) absorption bands of the following complexes have been recorded in digitised form: phenol (OH)- and phenol (OD)- dioxan in CCl4; phenol (OH)- and phenol (OD)-acetonitrile in CCl4; and phenol (OH)-acetonitrile in CDCl3. All these bands are broad and nearly featureless, and have widths at half height ranging from 75 to 148 cm?1. With one possible exception they appear to be free from Fermi resonances. By least-squares fitting of the theoretical bandshape function derived in part I to the experimental spectra we have been able to estimate the parameters Δ, ω2, and τC which characterise the theoretical autocorrelation function, and also to determine the vs(XH) stretching frequency very accurately. In the case of phenol (OD)-dioxan in CCl4 the discrepancies between the observed and fitted spectra can be entirely attributed to errors of observation. It is found that the Kubo parametér τC Δ is close to unity in all cases, showing that the vs(XH) bands are subject to partial (but not extreme) motional narrowing. The vσ(XH?Y) vibration is always heavily damped and has a broad spectral density. The changes in the spectral profiles produced by deuteration and change of solvent are easily understood in terms of the theory. Deuteration affects the amplitude of modulation, while changing the solvent affects the value of τC. In either case τCΔ changes, and the speed of modulation is altered. Since the system is far from the gaussian (slow modulation) limit, the bandshape changes markedly in consequence.  相似文献   

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