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1.
Semiconductivity and superconductivity in MoS2 (molybdenite) can be understood in terms of the band structure of MoS2. We present here the band structural properties of MoS2. The energy dependence of neff and εxeff is investigated. Using calculated values of neff and εxeff, the Penn gap has been determined. The value thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from the band structure. The Ravindra and Srivastava formula has been shown to give values for the isobaric temperature gradient of EG[(?EG?T)P], which are in agreement with the experimental data, and the contribution to (?EG?T)P due to the electron lattice interaction has been evaluated. In addition, the electronic polarizability has been calculated using a modified Lorentz-Lorenz relation.  相似文献   

2.
A study of opto-electronic properties of gallium chalcogenides (GaS, GaSe and GaTe) is presented here. An investigation into the various effective charge parameters (Zeff, e1s, e1Tand e1i and their correlation with ionicity have been done. The energy dependence of optical effective charge parameter (neff) have been discussed with respect to the band structure of respective chalcogenides. The low frequency optical dielectric constants (?00) have been derived using reflectivity data and the obtained values of ?00 have been found in agreement with the values obtained using Moss relation as also with the reported experimental data. The difference in the arrangement of fundamental structures of GaS and GaSe on one hand and GaTe on the other hand does not seem to effectively change the opto-eleetronic properties and the fundamental structure (which is common in all the three chalcogenides) is mainly responsible for determining these properties. The effect of surface conditions on the values of neff and ?∞ have been evaluated for GaTe. Using derived values of neff and ? the value of Penn gap have been determined. The Penn gap thus obtained is shown to be in agreement with the reflectivity data. In the passing we also show that essentially the Varshni formula explains fairly well the temperature dependence of the energy gap for gallium chalcogenides and the constants involved are evaluated.  相似文献   

3.
Infrared reflectivity spectra of p-type CuInTe2 single crystals were measured at room temperature for the polarization direction Ec and E | c in the wavenumber range from 55 to 4000 cm?1. Fits to a dielectric function including contributions from lattice oscillators and free carriers gave the first determination of the effective hole masses of mp⊥m0 = 0.85 and mp|m0 = 0.66. Two optical phonon modes were found for both polarization directions.  相似文献   

4.
The effect of pressure on the Curie temperature of the heavy rare-earth dialuminides has been measured up to 3.5 kbar. The derivatives dTc/dp are 0.00(4), 0.09, 0.21, 0.39, 0.60 and 0.71 K/kbar respectively for TmAl2 ErAl2, HoAl2, DyAl2, TbAl2 and GdAl2 thus indicating a clear positive correlation between dTc/dp and the de Gennes factor G. The results are discussed in terms of the RKKY model. However, the phenomenological parameter D/d, where D is the nearest-neighbour R-R distance and d the diameter of the 4f orbital, is used to reflect the non-δ-function character of the sf-coupling parameter Г. The experimental values of Г2D2 and Tp/G are found to decrease linearly with increasing D/d. This is in keeping with the RKKY proportionality of Tc?Tp to Γ2E?1FG. For GdAl2, TbAl2 and DyAl2 the quantity ? (dTcdp)kl(Dd)G coincides within the error limits with the slope of the Tp/G vs D/d plot.  相似文献   

5.
The fine structures of the (ν1 + ν2) and (ν2 + ν3) combination bands of ozone in the 5.7-μm region have been recorded and analyzed. The two vibrational states are coupled through Coriolis and second-order distortion terms. The interaction has been treated by the numerical diagonalization of the secular determinant for the two coupled states. With the centrifugal distortion parameters fixed to the ground state values, the following constants have been obtained: ν1 + ν2 = 1796.266, A110 = 3.6104, B110 = 0.44145, C1110 = 0.39029, ν2 + ν3 = 1726.526, A011 = 3.5537, B011 = 0.43982, C1011 = 0.38844, Y13 = ?0.466, and X13 = ?0.010 cm?1. In addition, the following anharmonic constants have been obtained: x12 = ?7.821 and x23 = ?16.494 cm?1. The value of the dipole moment ratio, R = 〈011|μz|0〉〈110|μx|0〉, is 1.30 ± 0.10.  相似文献   

6.
A frequency tunable infrared source has been constructed by using the (Ar-laser) - (dyelaser) difference frequency method developed by Pine and applied to the observation of the overtone bands of PH3 3ν2 ← 0 and 4ν2ν2 in the 3.4 μm region and 4ν2 ← 0 in the 1.6-μm region. A Stark modulation method was used to increase the sensitivity of detection. For transitions which were well modulated, the minimum detectable absorption coefficient was estimated to be ~3 × 10?7 cm?1 using a 3-m cell. Emphasis was placed on the observation of the A1-A2 splitting for K = 3n rotational levels. For the 3ν2 state splittings were observed for K = 3, 6, and 9 because PH3 is a very nearly spherical top in this state. The magnitude and the J dependence of the observed K = 3n splittings have been analyzed by using a normal symmetric rotor Hamiltonian and a centrifugal distortion term of the form τxxxz[(J+3 + J?3)Jz + Jz(J+3 + J?3)]4.  相似文献   

7.
Line strengths and self- and nitrogen-broadened half-widths were measured for spectral lines in the ν3 and ν2 + ν4 bands of 12CH4 and 13CH4 from 2870–2883 cm?1 using a tunable diode laser spectrometer. From measurements made over a temperature range from 215 to 297 K, on samples of 12CH4 broadened with N2, we deduced that the average temperature coefficients n, defined as bL0(T) = bL0(T0)(TT0)?n, of the Lorentz broadening coefficients for the ν3 and ν2 + ν4 bands of 12CH4 were 0.97 ± 0.03 and 0.89 ± 0.04, respectively. A smaller increase is observed in line half-width with increasing pressure for E-species lines, for both self- and nitrogen-broadening, than for other symmetry species lines over the range of pressures measured, 70 to 100 Torr.  相似文献   

8.
The E-B (0g+-0u+) band system of Br2 has been investigated at Doppler-limited resolution using polarization labeling spectroscopy. Merged E state data for the three naturally occurring isotopes in the range vE = 0–16, expressed in terms of the constants for 79Br2, are (in cm?1) Y0,0 = 49 777.962(54), Y1,0 = 150.834(22), Y2,0 = ?0.4182(28), Y3,0 = 6.6(11) × 10?4, Y0,1 = 4.1876(28) × 10?2, Y1,1 = ?1.607(16) × 10?4, and Y0,2 = 1.39(39) × 10?8. The bond distance is re = 3.194 A?, and the diabatic dissociation energy to Br+(3P2) + Br?(1S0) is 34 700 cm?1.  相似文献   

9.
The total νμ and νμ nucleon charged-current cross sections have been measured in BEBC filled with deuterium and exposed to the wide-band neutrino and antineutrino beams at the CERN-SPS. Assuming a linear energy dependence for the cross sections, σ = aE(?ν, we obtained the coefficients aνN = 0.62 ± 0.05 and aνN = 0.33 ± 0.03 (in units of 10?38 cm2/GeV), where the quoted error is mainly systematic. The ratio of the cross sections is σνNνN = 0.53 ± 0.03.We also determined the ratio of the charged-current cross section for neutrino interactions on neutrons and protons R = σνn/σνp = 2.10 ± 0.08 (statistical) ±0.22 (sysetmatic). The dependence of R on the variables x, y and Eν is discussed.  相似文献   

10.
The γ-decay of 26 resonances in the reaction 60Ni(p, γ)61Cu in the range Ep = 3690–3790 keV has been investigated. The g92 isobaric analogue state (IAS) corresponding to the parent state at E1 = 2114 keV in 61Mi has been resolved into several fine structure components. The absolute strength for the transition to the antianalogue state is found to be Γγ = 0.24 ± 0.07 W.u. The measured M1 strength distribution for the decay of the g92. IAS is compared to theoretical predictions.  相似文献   

11.
The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.  相似文献   

12.
Electroabsorption spectra of single crystals have been studied near the fundamental absorption edge at 77 and 300 K. At 300 K two positive peaks (2.34 and 2.42 eV) and a negative peak (2.38 eV) are observed in the electroabsorption spectrum. At liquid-nitrogen temperature a fine structure corresponding to the formation of a parabolic exciton (2.503 eV) is observed.Values of the width of the forbidden gap Eg, the n = 1 exciton positions, the exciton activation energy ΔEb, the effective Bohr radius aexc, the reduced effective mass of an electron-hole pair μ, and the exciton ionization field F(Eg = 2.535 eV, Eexc = 2.503 eV, Eb = 32 meV, aexc = 28AA;;;, μ = 0.15 m0, and F = 1.2 × 105 V cm-1) have been determined from the electroabsorption spectrum.  相似文献   

13.
Optical absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for 3T1g(F) band in Ni2+ and 4T2g(F) band in Co2+ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm-1 in the case of Ni2+ at low temperature has been interpreted to be the superposition of vibrational mode of SO2-4 radical on 3T1g(F) band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ.  相似文献   

14.
Using the 52Cr(t, p)54Cr reaction at a bombarding energy of 15 MeV, excitation energies have been measured for 30 levels up to Ex = 5.583 MeV in 54Cr. Angular distributions were obtained for all but one of these levels; these have been compared with distorted-wave Born approximation (DWBA) calculations to determine the L-transfer (and hence Jπ). The measured cross sections have been compared to the predictions of DWBA calculations that use two-neutron transfer amplitudes from a shell-model calculation with the active neutrons restricted to the (2p32, If52, 2p12) orbitals.  相似文献   

15.
The effective vibration-rotation Hamiltonians complete to fourth order in the Amat-Nielsen scheme for the upper states of the ν1, ν3, 2ν2, ν2 + ν4, and 2ν4 bands in methane are reviewed, and the major vibration-rotation interactions (H30, H?40, H?21, H31, H?22) connecting the different vibrational states are discussed. Explicit matrix elements in a basis of harmonic oscillator-symmetric rotor basis functions are given for the purely vibrational terms and for the vibration-rotation interactions. Expressions for spectral intensities of infrared and Raman spectra are presented, and the selection rules and transition moment matrix elements are stated. A computer program is described which, incorporating all these features, can be used for prediction of infrared and Raman spectra and for determination of molecular constants from observed spectra by a least-squares routine. As an example the program is applied to the 2ν4 isotropic Raman spectrum of 12CH4, leading to a very good agreement between the experimental and calculated spectra.  相似文献   

16.
The emission of Ni2+ ions in MgO, KMgF3, KZnF3 and MgF2 crystals has been investigated. The fine structure on the bands at about 20 000 cm-1 and 13 000 cm-1 has been studied in detail and from this and the excitation spectra these bands are assigned to 1T2g3A2g and 1T2g3T2g transitions respectively.  相似文献   

17.
The discrepancies concerning the optical and microwave values of B0 and D0 for the X3Σg? state of O2 have been removed by a nonlinear least-squares fit to all of the lines of the O2, b 1Σg+-X 3Σg? Red Atmospheric bands recorded by Babcock and Herzberg (Astrophys. J., 108, 167, 1948). The resulting values for B0″ and D0″ are in excellent agreement with the Raman and microwave values. Improved values are determined for B1″, D1″, γ1″ (spin-rotation), and ?1″ (spin-spin). Both γv″ and ?v″ increase in magnitude from v″ = 0 to v″ = 1. Improved Dunham Yi0 and Yi1 expansion coefficients are determined for the b 1Σg+ state, from which the Rydberg-Klein-Rees potential is constructed.  相似文献   

18.
The charge density wave transition in 2H-TaS2near 75 K has been observed to be incommensurate, using electron diffraction, with q1 = (0.338 ± 0.002)a10 along the 〈10.0〉 directions which, within the experimental uncertainty, remains temperature independent to about 14 K. Incommensurate charge density formation is also observed in AgxTaS2 samples for x?0.26 with an increase in q1 to (0.347 ± 0.002)a10 when x?0.26. Within the experimental error q1 appears to be temperature independent to 25 K.  相似文献   

19.
The magnetic phase diagram of FeCl2 · 2H2O has been determined by means of single crystal neutron diffraction experiments. Isothermal and isobaric measurements reveal the existence of first order and second order phase transitions separated by tricritical points at t11 = 0.5, h11 = 0.91 and t21 = 0.39, h21 = 0.99. Considerable hysteresis effects were observed at the antiferro—ferrimagnetic phase boundary at temperatures t < 0.33.  相似文献   

20.
The 0-0, 1-1, 2-2, and 3-3 bands of the A2Π-X2Σ+ transition of the tritiated beryllium monohydride molecule have been observed at 5000 Å in emission using a beryllium hollow-cathode discharge in a He + T2 mixture. The rotational analysis of these bands yields the following principal molecular constants.
A2Π:Be = 4.192 cm?1; re = 1.333 A?
X2Σ:Be = 4.142 cm?1; re = 1.341 A?
ωe′ ? ωe″ = 16.36 cm?1; ωe′Xe′ ? ωe″Xe″ = 0.84 cm?1
From the pure electronic energy difference (EΠ - EΣ)BeT = 20 037.91 ± 1.5 cm?1 and the corresponding previously known values for BeH and BeD, the following electronic isotope shifts are derived
ΔEei(BeH?BeT) = ?4.7 ≠ 1.5cm1, ΔEei(BeH?BeT) = ?1.8 ≠ 1.5cm1
and related to the theoretical approach given by Bunker to the problem of the breakdown of the Born-Oppenheimer approximation.  相似文献   

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