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1.
The equilibrium of the reaction galvinoxyl radical + 4,4′-methylene-bis(2,6-di-tert-butyl-phenol) (IOH) ⇆ hydrogalvinoxyl + 4,4′-methylene-bis(2,6-di-tert-butyl-phenoxyl radical) was monitored by electron paramagnetic resonance spectroscopy between 213 and 293 K. The equilibrium
constant was calculated for each temperature point and correlated to T
−1 applying the Van't Hoff relationship lnK
R = (−ΔH
R
0/RT) + (ΔS
R
0/R). The reaction enthalpy was found to be 12.0 ± 0.9 kJ/mol and the bond strength in IOH (BDE(O–H)) = 340.7 ± 3.0 kJ/mol. The thermochemical stabilization of the involved phenoxyls is discussed.
Authors' address: Sara N. Mendiara, Departamento de Química, Facultad de Ciencias Exactas y Naturales, Universidad Nacional
de Mar del Plata, Funes 3350, Mar del Plata 7600, Argentina 相似文献
2.
The third-order elastic constants of single crystal GaSb are determined using ultrasonic pulse interferometer at 10 MHz. The
constants at 300°K, in units of 1011 N.m.−2, are Cl11 = ™ 4 ·75 ± 0·06 C144 = + 0·50 ± 0·25 C113 = ™ 3 ·08 ± 0·02 C166 = ™ 2·16 ± 0·13 C123 = ™ 0 ·44 ± 0·29 C456 = ™ 0·25 ± 0·15 These constants are used to evaluate the three anharmonic first and second neighbour force constants based
on modified Keating’s model. The constants are (in units of 1011 N.m−2)γ=− 2·406;δ=0·407;ε=−0·222. 相似文献
3.
The phase boundary of the binary liquid system CS2+CH3NO2 is studied over nearly six decades in reduced temperature 3×10−6<ε=(T
C−T)/T
C<2×10−1 and over the composition range 8-98 mole % of CS2. The critical parameters areT
C=335.132K andx
C=57.34 mole % of CS2. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromT
C. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromT
C. NearT
C, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε7/8 exp (−gε
h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms
of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much
weaker in a liquid-gas system and hence might have escaped detection. 相似文献
4.
Suresh Chandra 《Pramana》2004,62(5):1181-1185
Kaur and Mahajan [1] have claimed to derive a universal relation InG = 1.91578(±0.09727) + 0.97111(±0.03809) In Δ between the Sutherland parameter Δ(=ω
er
e
2
/2De) and the dimensionless parameterG(= 8ω
exe/Be) for the ground as well as excited electronic states of diatomic molecules. Validity of this relation is checked and we find
that the relation is not correct. Next, we checked the validity of the relation Δ = 2.2re for the alkali group diatomic molecules. This relation is also found not to be correct. 相似文献
5.
M. A. Anisimov A. V. Bogach V. V. Glushkov S. V. Demishev N. A. Samarin V. B. Filipov N. Yu. Shitsevalova A. V. Kuznetsov N. E. Sluchanko 《Journal of Experimental and Theoretical Physics》2009,109(5):815-832
The magnetoresistance Δρ/ρ of single-crystal samples of praseodymium and neodymium hexaborides (PrB6 and NdB6) has been measured at temperatures ranging from 2 to 20 K in a magnetic field of up to 80 kOe. The results obtained have
revealed a crossover of the regime from a small negative magnetoresistance in the paramagnetic state to a large positive magnetoresistive
effect in magnetically ordered phases of the PrB6 and NdB6 compounds. An analysis of the dependences Δρ(H)/ρ has made it possible to separate three contributions to the magnetoresistance for the compounds under investigation. In
addition to the main negative contribution, which is quadratic in the magnetic field (−Δρ/ρ ∝ H
2), a linear positive contribution (Δρ/ρ ∝ H) and a nonlinear ferromagnetic contribution have been found. Upon transition to a magnetically ordered state, the linear
positive component in the magnetoresistance of the PrB6 and NdB6 compounds becomes dominant, whereas the quadratic contribution to the negative magnetoresistance is completely suppressed
in the commensurate magnetic phase of these compounds. The presence of several components in the magnetoresistance has been
explained by assuming that, in the antiferromagnetic phases of PrB6 and NdB6, ferromagnetic nanoregions (ferrons) are formed in the 5d band in the vicinity of the rareearth ions. The origin of the quadratic contribution to the negative magnetoresistance is
interpreted in terms of the Yosida model, which takes into account scattering of conduction electrons by localized magnetic
moments of rare-earth ions. Within the approach used, the local magnetic susceptibility χloc has been estimated. It has been demonstrated that, in the temperature range T
N < T < 20 K, the behavior of the local magnetic susceptibility χloc for the compounds under investigation can be described with good accuracy by the Curie-Weiss dependence χloc ∝ (T − Θ
p
)−1. 相似文献
6.
T. Sasanuma A. Taniguchi M. Tanigaki Y. Ohkubo Y. Kawase 《Hyperfine Interactions》2004,159(1-4):251-255
The g-factor of the first excited state of 93Sr (E = 213 keV, T
1/2 = 4.6 ns) was measured by an on-line TDPAC technique with use of the strong hyperfine field in Fe metal. The Larmor frequency
ω
L = (2.60 ± 0.15) × 108 rad/s was obtained. The g-factor is derived as g = −0.227 ± 0.013 from g = −ℏω
L/B
hf
μ
N. If the spin of the first excited state of 93Sr is assumed to be 3/2, the g-factor is predicted by a simple core-excitation model as g = −0.22, which is in good agreement with the present experimental result. 相似文献
7.
The spectral dependence of the electron-phonon relaxation rate γe−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation
of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γe−ph(ℏω) near the Fermi level E
F
, using the parametrization γe−ph(ℏω)∝λ〈Ω2〉 (ℏω−E
F
)2 makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω2〉. The parameter λ〈Ω2〉 for YBa2Cu3O7−δ is analyzed using this method.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999) 相似文献
8.
S. A. Astashkevich B. P. Lavrov A. V. Modin I. S. Umrikhin 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(1):16-31
A statistical analysis of the available literature data and data obtained in this work on the wave numbers of the lines that
appear in triplet-triplet rovibronic transitions of the H2 molecule was performed. This allowed us to verify and refine the controversial identification of spectral lines and find
the optimum rovibronic level energy values for the c
3Π
u
±, r
3Π
g
−, and s
3Δ
g
− states. The ratios between the line strengths of the P, Q, and R branches of the (4dπ)r
3Π
g
−, (4dδ)s
3Δ
g
− → (2pπ)c
3Π
u
± band systems of the H2 molecule were measured systematically. The calculation results obtained in the Frank-Condon approximation differed substantially
(by up to two orders of magnitude) from the experimental data. The dependences of the ratios between rovibronic line strengths
of the r
3Π
g
− → c
3Π
u
± and s
3Δ
g
− → c
3Π
u
± transitions on the rotational quantum number N′ of the upper level were found to correlate with each other. The deviations of adiabatic theory increase as N′ grows, which is evidence of an important role played by electronic-rotational interactions in the perturbation of transition
probabilities. The experimental ratios between the probabilities of rovibronic transitions satisfactorily agree with the results
of calculations within the framework of the simple nonadiabatic model taking into account electronic-rotational interaction
of radiating adiabatic states in the approximation of pure precession. The dependences of transition probabilities on N′ were obtained for the first time for the first four diagonal bands of the r
3Π
g
−, s
3Δ
g
− → c
3Π
u
± transitions.
Original Russian Text ? S.A. Astashkevich, B.P. Lavrov, A.V. Modin, I.S. Umrikhin, 2008, published in Khimicheskaya Fizika,
2008, Vol. 27, No. 2, pp. 22–38. 相似文献
9.
S. F. Baranovskii P. A. Bolotin M. P. Evstigneev 《Journal of Applied Spectroscopy》2006,73(2):171-177
We have studied self-association of aromatic molecules of the thiazine dye methylene blue in aqueous solution, using a dimer
model. We have determined the dimerization equilibrium constant for the dye molecules KD = 3900 ± 800 M−1 at T = 293 K. We have decomposed the experimental spectrum into dimer and monomer components. Using the ratio of the molar
absorption coefficients for two absorption bands of the dimer spectrum, we obtained the “average” value of the angle between
the electronic transition moments of the molecules in the dimers, α = 48°.
We have studied heteroassociation of methylene blue (MB) and 1,3,7-trimethylxanthine (caffeine) molecules in aqueous solution.
We have calculated the heteroassociation constant as 200 ± 34 M−1. We conclude that heteroassociation of methylene blue and caffeine molecules leads to a lower effective dye concentration
in solution, which hypothetically may affect its biological activity.
We have determined the values of the Gibbs free energy, the enthalpy, and the entropy for dimerization of methylene blue molecules:
ΔG293 = −(20 ± 3) kJ/mol, ΔH = −(25 ± 9) kJ/mol, Δ S293 = −(17 ± 6) J/mol·K; and for methylene blue-caffeine heteroassociation: ΔG293 = −(13 ± 3) kJ/mol, ΔH = −(14 ± 10) kJ/mol, ΔS293 = −(2.4 ± 0.2) J/mol·K, respectively. We have shown that the methylene blue aggregates and the heteroassociates with caffeine
are predominantly stabilized by dispersion interactions between the chromophore molecules in the associates.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 158–163, March–April, 2006. 相似文献
10.
Yu. A. Aleshchenko A. V. Muratov V. M. Pudalov E. S. Zhukova B. P. Gorshunov F. Kurth K. Iida 《JETP Letters》2012,94(9):719-722
The results of infrared reflectivity measurements for the iron-based high-temperature superconductor Ba(Fe0.9Co0.1)2As2 are reported. The reflectivity is found to be close to unity at frequencies ω lower than 2Δ/h (2Δ is the superconducting gap and h is Planck’s constant). This is evidence for the s
+/− or s
+/+ symmetry of the superconducting order parameter in the studied compound. The infrared reflectivity spectra of Ba(Fe0.9Co0.1)2As2 manifest opening of several superconducting gaps at temperatures lower than critical T
c
. 相似文献
11.
In order to remove some of the unsatisfactory features of the GIM model, we consider15-admixture in SU(4). ΔC=±ΔS decays remain unaffected. Lee-Sugawara sum-rule is obtained.15-admixture is extended then to63-admixture in SU(8). The most general Hamiltonian (H
w∼63⊕720⊕1232) in SU(8) is found to give Lee-Sugawara relation and Σ+
+=0 forS-wave decays of uncharmed baryons. Decay amplitude relations for ΔC=−1, ΔS=0 mode are obtained. 相似文献
12.
E. Korotyaev 《Communications in Mathematical Physics》1997,183(2):383-400
LetG
n=(A
n
−
, A
n
+
),n≧1, denote the gaps,M
n
±
be the effective masses and Σn=[A
n−1
+
,A
n
-
],A
0
+
=0, be the spectral bands of the Hill operatorT=−d
2/dx
2+V(x) inL
2 (R), whereV is a 1-periodic real potential fromL
2(0,1). Let the length gapL
n=|Gn|, hn be the height of the corresponding slit on the quasimomentum domain and Δn=π2(2n−1)−∣Σn∣>0 be the band reduction. Let
,n≧1, denote the gap length for the operator
. Introduce the sequencesL={Ln}, h={hn}, l={ln}, Δ={Δn},M
±={M
n
±
} and the norms
,m≧0. The following results are obtained: i) The estimates of‖V‖, ‖L‖, ‖h‖
1, ‖l‖1, ‖δ‖ in terms of ‖M±‖2, ii) identities for the Dirichlet integral of quasimomentum and integral of potentials and so on, iii) the generation of
i), ii) for more general potentials.
The research described in this publication was made possible in part by grant from the Russian Fund of Fundamental Research
and INTAS. 相似文献
13.
S.N. Nakamura K. Bartlett G.A. Beer G.R. Gill R.S. Hayano T.M. Ito M. Iwasaki L. Lee G. Mason A. Olin H. Outa M. Salomon R. Seki T. Taniguchi T.P. Terada G. Trayling Y. Yamashita S. Yen 《Hyperfine Interactions》1999,118(1-4):45-51
We successfully observed clear K-series kaonic hydrogen X-rays for the first time taking advantage of two charged pions tagging technique and a gaseous hydrogen
target. The strong-interaction energy shift and width of 1s state of K
−p atom were determined to be ΔE
1s
= -323 ± 63 (statistical) ± 11 (systematic) eV and Г1s = 407 ± 208 ± 100 eV. Our result means that the K
−p strong interaction near threshold is repulsive and the long-standing kaonic hydrogen puzzle is solved.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
Experimental data on the spin-exchange rate constants for the He(23
S
1)-Na(32
S
1/2) system are reported for the first time. Measurements show that the spin-exchange rate constant is C
se
= (23 ± 11) × 10−10 cm3 s−1 and the chemical ionization rate constant is C
si
= (29 ± 14) × 10−10 cm3 s−1 at a temperature of 420 K. The results are compared with the data calculated from the rate constants. 相似文献
15.
R. Yu. Abdulsabirov I. I. Antonova S. L. Korableva N. M. Nizamutdinov V. G. Stepanov N. M. Khasanova 《Physics of the Solid State》1997,39(3):423-425
The orientational dependences of the EPR spectra of Fe3+-doped LiCaAlF6 single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail.
The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B
20=40.072×10−4 cm−1, B
40=−5.799×10−4 cm−1, B
43=−4.281×10−4 cm−1, A
s=24.33±1, A
p=6.13±1, g
∥=g
⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well
when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F−).
Fiz. Tverd. Tela (St. Petersburg) 39, 488–490 (March 1997) 相似文献
16.
Approximating the shape of the magneto-thermoelectric power (TEP) ΔS(T,H) measured in Bi2Sr2CaCu2Oy by an asymmetric linear triangle of the form ΔS(T,H)≃S
p
(H)±B
±(H)(T
c
−T) with positive B
−(H) and B
+(H) defined below and above T
c
, we observe that B
+(H) ≃2B
−(H). To account for this asymmetry, we explicitly introduce the field-dependent chemical potential μ(H) of holes into the Ginzburg-Landau theory and calculate both an average ΔS
av(T,H) and fluctuation contribution ΔS
fl(T,H) to the total magneto-TEP ΔS(T,H). As a result, we find a rather simple relationship between the field-induced variation of the chemical potential in this
material and the above-mentioned magneto-TEP data around T
c
, viz. Δ μ(H)∝S
p
(H).
Zh. éksp. Teor. Fiz. 116, 257–262 (July 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
17.
D. É. Fel’dman 《Journal of Experimental and Theoretical Physics》1999,88(6):1170-1178
The critical behavior of the transverse (with respect to the field) magnetization component in classical degenerate magnets
with only nearest-neighbors interaction in a uniaxial random magnetic field at zero temperature is found exactly. For a Gaussian
distribution of the random field the asymptotic transverse magnetization in strong fields does not depend on the dimension
of the space and is of the form m
⊥ ∝ 1nh
0/h
0
2
, where h
0 is the width of the distribution. For a bimodal distribution, where only the field direction is random and the amplitude
is fixed, the transverse magnetization behaves as m
⊥∝exp(−const/(H
c
−H)
D/2), where H is the amplitude of the random field, D is the dimension of the space, and H
c
is the critical field.
Zh. éksp. Teor. Fiz. 115, 2143–2159 (June 1999) 相似文献
18.
V. V. Popov P. P. Konstantinov Yu. V. Rud’ 《Journal of Experimental and Theoretical Physics》2011,113(4):683-691
Electrical resistivity ρ and Hal coefficient R are measured as a function of the temperature (T = 1.7−310 K) and the magnetic field (up to H = 28 kOe) in zero-gap semiconductor CuFeS2 samples subjected to hydrostatic compression and under various heat-treatment conditions. At low temperatures, anomalies
are observed in the kinetic effects related to the presence of ferromagnetic clusters: the magnetoresistance at T = 4.2 K and T = 20.4 K acquires a hysteretic character and thermopower α changes its sign at T < 15 K. The temperature dependence of conduction-electron concentration n in CuFeS2 has a power form in the temperature range T = 14−300 K, which is characteristic of the intrinsic conductivity in zero-gap semiconductors. In CuFeS2, we have n(T) ∝ T
1.2; in isoelectron compound Cu1.13Fe1.22Te2, we have n(T) ∝ T
1.93. Heat treatment is found to affect the intrinsic conductivity of CuFeS2, as the action of hydrostatic compression (carrier concentration changes); that is, the carrier concentration changes. However,
a power form of the n(T) and ρ(T) dependences is retained. 相似文献
19.
Kinetic regularities and mechanism of polymerization of perfluoromethylvinyl ether at high pressures
A. A. Zharov O. K. Nikolaeva 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(5):839-845
The kinetics of the thermal polymerization of perfluoromethylvinyl ether (PFMVE) is studied at pressures of 3–13 kbar (300–1300
MPa) and temperatures of 80–260°C. The activation energy (E
act = (76 ± 3) kJ/mol) and activation volume (ΔV0⪼ = −(27 ± 2) cm3/mol) for the overall polymerization rate are determined. The inhibition method is used to estimate the activation energy
of thermal initiation (E
in = (79.9 ± 3) kJ/mol). The quantity E
p
− (1/2)E
t
was calculated to be 36.6 ± 3 kJ/mol. The limiting polymerization temperature was evaluated: T
lim = (180 ± 3)°C. A mechanism of PFMVE polymerization is proposed on the assumption that the reaction is bimolecular. 相似文献
20.
Giulio Gambarota H. W. M. van Laarhoven M. Philippens W. J. M. Peeters P. Rijken A. van der Kogel C. J. A. Punt A. Heerschap 《Applied magnetic resonance》2010,38(3):349-360
The objective of this study is to assess whether ultrasmall superparamagnetic iron oxide (USPIO)-induced changes of the water
proton longitudinal relaxation rate (R
1) provide a means to assess blood hemodynamics of tumors. Two types of murine colon tumors (C26a and C38) were investigated
prior to and following administration of USPIO blood-pool contrast agent with fast R
1 measurements. In a subpopulation of mice, R
1 was measured following administration of hydralazine, a well-known blood hemodynamic modifier. USPIO-induced R
1 increase in C38 tumors (ΔR
1 = 0.072 ± 0.0081 s−1) was significantly larger than in C26a tumors (ΔR
1 = 0.032 ± 0.0018 s−1, N = 9, t test, P < 0.001). This was in agreement with the immunohistochemical data that showed higher values of relative vascular area (RVA)
in C38 tumors than in C26a tumors (RVA = 0.059 ± 0.015 vs. 0.020 ± 0.011; P < 0.05). Following administration of hydralazine, a decrease in R
1 value was observed. This was consistent with the vasoconstriction induced by the steal effect mechanism. In conclusion, R
1 changes induced by USPIO are sensitive to tumor vascular morphology and to blood hemodynamics. Thus, R
1 measurements following USPIO administration can give novel insight into the effects of blood hemodynamic modifiers, non-invasively
and with a high temporal resolution. 相似文献