N2 Laser Excited Fluorescence of Oxalyl Chloride at 77°K

The N₂ laser excited fluorescence spectrum and the intensity of fluorescence of oxalyl chloride C₂O₂Cl₂) condensed at 77°K either alone, or, diluted with a non-hydrocarbon or a hydrocarbon with dilution ratios ranging from 10 to 100 were studied. A slow condensation of the hydrocarbon matrix diluted sample showed a considerable reduction in the fluorescence intensity as compared to a fast condensation of the same sample.     

Characteristic features of carbazole phosphorescence quenching by benzophenone molecules in toluene at 77 K

We have studied the characteristic features of carbazole phosphorescence quenching by benzophenone in toluene at 77 K. We have shown that the decrease in the relative phosphorescence intensity for carbazole (energy donor) by a greater factor than we see for the relative change in its decay time is due to the fact that a change in the phosphorescence decay time occurs only for carbazole molecules participating in triplet-triplet energy transfer, while the substantial decrease in the phosphorescence intensity for carbazole with no change in the phosphorescence decay time is connected with quenching of its singlet states. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 554–556, July–August, 2006.     

On the concentration dependence of the sensitized phosphorescence quantum yield of naphthalene in toluene at 77 K

A concentration dependence of the sensitized phosphorescence quantum yield of naphthalene (with benzophenone as a donor) in equimolar toluene solutions at 77 K is studied for concentrations of components ranging from 0.1 to 0.5 mole/litre. A nonmonotonic character of this dependence is established. With increasing solution concentration, intervals of increase (from 0.1 to 0.35) and decrease (from 0.35 to 0.5) of the sensitized phosphorescence quantum yield are observed. Reasons for this dependence are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–6, October, 2004.     

Characteristic features of the phosphorescence of the complex “naphthalene-d8-β-cyclodextrin” at 77 K

It is found that the phosphorescence of naphthalene-d8 in an inclusion complex in crystalline β-cyclodextrin at 77 K differs substantially from that of frozen homogeneous solutions: The vibrational structure of the spectrum is better-resolved, the Stokes shift in the spectrum is smaller, and the lifetime is longer than the values known previously. Similar effects are observed for naphthalene-h8 and phenanthrene. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 507–510 (10 April 1997)     

Photomagnetic effect in n-type InSb at 77 °K

The steady-state odd photomagnetic effect was studied at liquid-nitrogen temperatures (77 °K) in n-type InSb having a carrier density of 4.2 · 10¹⁶ cm^-3. When the rate of surface recombination on the illuminated surface is higher than on the dark surface, the photomagnetic effect becomes negative in suitable magnetic fields.Translated from Izvestiya VUZ. Fizika, No. 7, pp. 28–31, June, 1970.The authors thank V. A. Gridin for useful discussions.     

Observations of the ac Josephson effect in Y-Ba-Cu-O superconductors at 77 K

The observations of the ac Josephson effect in Y-Ba-Cu-O superconducting weak link were reported. The Y-Ba-Cu-O sample had a Tc=90 K. The I–V characteristics of the weak link junction were mearsured at 77 K. The junction had a Ic=0.43 mA and the normal resistance Rn=0.38 ohm. 10.15 GHz microwave was applied to the junction and the rf-induced steps up to n=10 were observed. The dependence of the step height on the rf level was in agreement with ordinary Josephson tunneling behavior.     

High electric-field hall effect measurements onn-type InSb at 77 K

Pulsed Hall-effect experiments onn-type InSb at 77 K, with nanosecond time resolution, at magnetic inductions down to 2 mT and for electric field strengths up into the avalanche regime are reported. Results on mobility are compared with previous experimental data and various theoretical calculations. For the first time also results on the scattering factor as a function of electric field are given. A curious time dependent behaviour of the transverse voltage under avalanche conditions is reported. Along with the development of the avalanche the transverse voltage decreases and may even change sign. This phenomenon is qualitatively explained in terms of the magnetoconcentration effect and the change of contact properties under avalanche conditions.     

Line phosphorescence spectrum of octachlorodibenzo-p-dioxine at 4.2 K

The line phosphorescence spectrum of octachlorodibenzo-p-dioxine (OCDX) is obtained and interpreted. The symmetry of the lowest triplet state of this molecule is established. The vibrational frequencies found from the vibronic phosphorescence spectrum at 4.2 k are assigned to the vibrational modes of certain symmetry related to individual functional atomic groups of the molecule. The relation between contributions from the spin-orbit (SO) and vibronic-spin-orbit (VSO) interactions to the phosphorescence rate constant k _ph of the OCDX molecule is found from the vibronic line intensities. It is found that the increase in the number of Cl atoms in OCDX compared to that in tetrachlorobenzo-p-dioxine results in the increase in the relative contribution of the VSO interaction to k _ph.     

Nonradiative deactivation of the lowest triplet state of naphthalene and its hydroxy derivatives at 77 K

The validity of an inductive resonance theory of energy transfer from the T ₁→S ₀ transition dipole to overtone vibrations of molecular groups containing H and D atoms is experimentally tested for a series of compounds whose conjugation systems are similar in size. To this end, by using kinetic, spectral, and luminescent methods (measurements of the phosphorescence decay times, phosphorescence spectra, ratios between the quantum yields of phosphorescence and fluorescence at 77 K, total quantum yields of fluorescence at 293 K, and ratios between the quantum yields of fluorescence at 293 and 77 K), the deactivation processes of the lowest excited T ₁ and S ₁ states of seven emitting centers (naphthalene, its hydroxy and dihydroxy derivatives, and their monoanions) in solutions in ethanol-h ₆, ethanol-d ₆, and their 2: 1 mixtures with diethyl ether are studied. For all the compounds studied, the rate constants k _r of the radiative T ₁→S ₀ transition and the changes in the overlap integrals of the spectra of phosphorescence and absorption of overtones of CH stretching vibrations are determined. The rate constants of energy transfer k _dd(CH) from the T ₁→S ₀ transition dipole to the stretching vibrations of the CH bonds are calculated without regard for the changes in the localization and orientation of this transition dipole in the compounds under study. The contribution of an individual CH group k _nr(CH) to the total rate constant of nonradiative deactivation of the T ₁ state averaged over the CH groups of the naphthalene ring system is ascertained. A good correlation between the changes in the constants k _nr(CH) and k _dd(CH) in the series of the hydroxy derivatives of naphthalene is found, which is indicative of the inductive resonance mechanism of the energy degradation of the T ₁ state. The deviations from proportionality between the changes in these constants upon passing from naphthalene to its hydroxy derivatives, which correlate with a marked increase in the radiative constant k _nr of the hydroxy derivatives in comparison with naphthalene, indicate changes in the strength and localization of the T ₁→S ₀ transition dipole moment and in its orientation with respect to the plane of the molecule that occur due to introduction of a heteroatom, oxygen, whose lone pair of electrons enters into conjugation with the πelectrons of the naphthalene ring system.     

Excited State Proton Transfer Reaction of 4-Methyl-2,6-dicarbomethoxyphenol in Some Protic Solvents at Room Temperature and 77K: Interaction with Base

The ground and excited state proton transfer reactions of 4-methyl-2,6-dicarbomethoxyphenol (CMOH) have been studied in water and some alcoholic solvents both in the presence and in the absence of base by means of absorption, emission, and nanosecond spectroscopy at room temperature and 77 K. Solute–solvent interaction appears to play a major role in determining the nature of absorbing and fluorescing species in these solvent media. The emission properties of CMOH have been examined in relation to those of 4-methyl-2,6-diformylphenol (MFOH). The spectral characteristics obtained indicates that CMOH in methanol, ethanol, and water exists in more than one structural form in both the ground and excited states. At 77 K the emission spectra show phosphorescence only in the presence of a base. The fluorescence decay rates of CMOH are relatively slower than those of MFOH and nonradiative decays are dominant in the decay process of CMOH. It is proposed that intramolecular hydrogen bond in CMOH is stronger compared to that in MFOH. From our theoretical calculation at AM1 level of approximation suggested that the process is thermodynamically endothermic in the ground state and also encounter high barriers. However, the process becomes exothermic in the excited state.     

The adsorption of argon on ZnO at 77 K

We have studied the adsorption of argon onto ZnO surfaces at 77 K by means of quasi-equilibrium adsorption volumetry coupled with high resolution microcalorimetry and Grand Canonical Monte-Carlo (GCMC) simulations. The adsorbate/surface adsorption potential function (PN type) used in the simulations, was determined on the basis of ab initio calculations (corrected for dispersion interactions). The first aspect of this work was to test the ability of a standard solid-state Hartree—Fock technique coupled with a perturbative semi-empirical approach in deriving a reliable adsorption potential function. The dispersion part of the adsorbate/surface interatomic potential was derived by using perturbation theory-based equations while the repulsive and induction interactions were derived from periodic Hartree—Fock (CRYSTAL92) calculations. GCMC simulations based on this adsorption potential allow one to calculate adsorption isotherms and isosteric heat versus loading curves as well as singlet distribution functions at 77 K for each type of ZnO (neutral and polar) faces. The combined analysis of the simulation data for all surfaces gives a good insight of the adsorption mechanism of argon onto ZnO surfaces at 77 K in agreement with experiment. As far as neutral surfaces are concerned, it is shown that adsorption first takes place within the ‘troughs’ which cover ZnO neutral surfaces. At low chemical potentials, these semi-channels are preferential adsorption sites in which we could detect a nearly one-dimensional adsorbate freezing in a commensurate phase at 77 K. The polar O faces are the most favourable surfaces for adsorption at higher chemical potentials.     

Neutron scattering study of NiHx at 77K

The results of simultaneous measurements of inelastic incoherent neutron scattering (IINS) and neutron diffraction on NiH_x system with x = 0.40, 0.28 and 0.12 at temperatures of 77 K are briefly presented. In the phonon density of states, supposing a one-phonon mechanism for the scattering process, the optic modes appear as a broad band from 70 to 140 meV with a strong peak at 90 meV and weak peaks at 105 and 130 meV. Neutron diffraction confirms information about the phase composition of the samples investigated.     

纳米Ni在77 K温度下压缩行为的研究

利用低温力学测试系统研究了电化学沉积纳米Ni在77 K温度下的压缩行为. 室温下纳米Ni 的屈服强度为 2.0 GPa, 77 K温度下的屈服强度为3.0 GPa, 压缩变形量则由室温的10%左右下降到5%. 借助应变速率敏感指数、激活体积、扫描电子显微和高分辨透射电子显微分析, 对纳米Ni的塑性变形机制进行了表征. 研究表明, 在77 K温度下的塑性变形主要是由晶界-位错协调变形主导, 晶界本征位错弓出后无阻碍地在晶粒内无位错区运动, 直至在相对晶界发生类似切割林位错行为. 同时分析了弓出位错的残留位错部分在协调塑性变形时起到的增加应变相容性和减小应力集中的作用. 利用晶界-位错协调机制和残留位错运动与温度及缺陷的相关性揭示了纳米Ni室温和77 K温度压缩性能差异的内在原因. 关键词： 塑性变形 强度 位错     

Radiolysis of vitreous cyclohexane-neohexane mixtures at 77 K

Vitreous mixtures of cyclohexane and neohexane were irradiated by gamma rays at 77 K. The relative radical concentrations were computed from E.S.R. spectra of the irradiated mixtures. A chemical activation transfer from the neohexane to the cyclohexane can explain the excess of cyclohexyl radicals with respect to the electron fraction.

An hydrogen transfer from neohexane to cyclohexyl radicals occurs at 120 K.