Raman and infrared spectra of CdIn2S4 and ZnIn2S4

Four one-phonon Raman lines have been found in CdIn₂S₄ (ZnIn₂S₄) spinels at 92 (72) cm^-1, 186 (184) cm^-1, 246 (253) cm^-1, and 367 (372) cm^-1 for incident photon energies well below the energy gap E_G ～ 2.4 (2.2) eV at 300 K. For photon energies close to E_G, the 367 cm^-1 mode underwent a resonant enhancement in CdIn₂S₄ and four infrared active but Raman forbidden F_1u modes appeared in the CdIn₂S₄ and ZnIn₂S₄ Raman spectra: TO modes at 226 (221) cm^-1 and 309 (312) cm^-1, and LO modes at 274 (272) cm^-1 and 340 (342) cm^-1.     

Raman spectroscopy of RuSr2(Eu1.5Ce0.5)Cu2O10 magneto-superconductor

Raman spectroscopy studies are reported for the RuSr₂Eu_1.5Ce_0.5Cu₂O₁₀ (Ru-1222) compound at various temperatures of 300, 250, 200 and 90 K. Three distinct vibrational bands: the first at 110, 140, and 160 cm⁻¹, the second at 295 and 347 cm⁻¹, and third one at 651 cm⁻¹ are seen in Raman spectra of the compound at room temperature. These bands are attached to the Cu atoms’ c-direction, the Ru atoms’ ab-plane stretching and Ru atoms’ c-direction anti-stretching modes. Below 200 K, an extra vibrational mode is also seen at 260 cm⁻¹. Also, with a decrease in temperature, though the Cu vibrational modes remain intact, the Ru atoms’ ab-plane stretching (295 cm⁻¹) and c-direction anti-stretching (651 cm⁻¹) modes shift gradually to higher wave number positions. The frequencies of modes at 260 and 651 cm⁻¹ showed anomalous softening and line-width broadening below 100 K that corroborates well with the spin ordering seen in susceptibility studies. The studied compound is a ferromagnetic superconductor with magnetic ordering of the Ru spins at 200 K and superconductivity below 30 K. A magnetic and electrical transport characterization of the compound is also presented briefly.     

Laser-Raman spectroscopy of living cells

Investigations into the laser—Raman shift spectra of bacterial and mammalian cells have revealed that many Raman lines observed at 4–6 K, do not appear in the spectra of cells held at 300 K. At 300 K, Raman activity, at set frequencies, is observed only when the cells are metabolically active; however, the actual live cell spectrum, between 0 and 3400 cm^?1, has been found to alter in a specific way with time as the cells' progress through their life cycles. Lines above 300 cm^?1, from in vivo Raman active states, appear to shift to higher wave numbers whereas those below 300 cm^?1 seem to shift to lower ones. The transient nature of many shift lines observed and the intensity of them when present in the spectrum indicates that, in vivo, a metabolically induced condensation of closely related states occurs at a set time in the life of a living cell. In addition, the calculated ratio between the intensities of Stokes and anti-Stokes lines observed suggests that the metabolically induced “collective” Raman active states are produced, in vivo, by non thermal means. It appears, therefore, that the energetics of the well established cell “time clock” may be studied by laser—Raman spectroscopy; moreover, Raman spectroscopy may yield a new type of information regarding the physics of such biological phenomena as nutrition, virus infection and oncogenesis.     

Optic-mode coupling in ferroelectric gadolinium molybdate

Separate measurements of the A₁(TO) and A₁(LO) Raman spectra of ferroelectric gadolinium molybdate at 80°K and above have elucidated the origin of the anomalous temperature dependence of the two lowest frequency lines in the A₁(TO) spectrum. The observed behavior is postulated to be the result of coupling among modes at 44.5, 51.5, and 83 cm^?1 (at 80°K). The 44.5 and 83 cm^?1 modes become the degenerate, soft zone-boundary modes of the paraelectric phase while the 51.5 cm^?1 mode changes to B₂ symmetry. The two lowest frequency lines are the same as those observed previously in i.r. absorption.     

A comparative performance evaluation of micro-Raman spectrograph using holographic notch filter and dielectric filter

An indigenously designed and developed micro-Raman spectrograph, consisting of a diode-pumped solid-state green laser for the excitation of Raman scattering, a Raman imaging microscope, CCD as a detector and a notch filter, has been extensively studied to evaluate its performance. A dielectric edge filter (having 27 alternate layers of SiO₂ and TiO₂) and a holographic notch filter (Oriel make) have been used to block the Rayleigh scattered light from the sample to the entrance slit of the spectrograph. Holographic notch filter is found to be able to record the Raman shifts below 700 cm⁻¹ conveniently whereas dielectric edge filter (27 layers) has enabled the spectrograph to record the Raman spectra very efficiently after a wave-number shift of 700 cm⁻¹. It has also been observed that the instrument using the edge filter provides a peculiar spectrum consisting of three spectral lines having Raman shifts as 569, 1328 and 1393 cm⁻¹ in the Raman spectrum of a weakly scattering sample with large reflectivity. Similarly, a spectrum consisting of multiple lines has been observed when the instrument is being operated using a holographic notch filter. These spectral lines are not observed in the case of liquid samples such as benzene, carbon tetrachloride, ethanol, diethyl ether etc. The origin of these peculiar spectral lines has been briefly discussed in the paper. Additionally, a major motivation for this work is to utilize the results for the selection of an appropriate filter depending on the type of the sample, i.e. weakly scattered and highly reflecting sample or highly scattered and low reflecting sample.     

Temperature-dependent light scattering from magnetic excitons in TlCoF3

Raman spectra of antiferromagnetic thallium cobaltous fluoride have been obtained with 4579A argon ion laser excitation at temperatures from 4°K to T_N = 94 ± 2°K. The features observed consist of six Co²⁺ excitons ranging in energy from 325 to 1070 cm^-1, at two-magnon peak with low-temperature energy of 315 cm^-1, and a one-magnon feature whose 4°K energy is 37 cm^-1. The energy and linewidth of the one-magnon scattering has been measured from 4°K to about 0.8 T_N; it is found that the magnon becomes critically damped at about 0.8 T_N, in good agreement with our previous observations on RbCoF₃. The Co²⁺ excitons observed at 325, 380, 410, 730 (weak), 960, and 1070 cm^-1 agree in energy quite well with the KCoF₃ levels calculated by Buyers, Holden et al. as 340, 400, 467, 767, 967 and 1050 cm^-1.     

Raman and infrared spectra of ZnSiAs2

The optical phonons at k = 0 of ZnSiAs₂ have been investigated by Raman scattering and infrared reflectivity measurements at 300 K. Eleven of thirteen expected optically active phonons have been observed and identified with respect to their symmetry types. The phonon frequencies appear in the range from 415 cm^-1 to 75 cm^-1 with predominant polar modes at 400 cm^-1 (gG₅), 389 cm^-1 (Γ₄) and 242 cm^-1 (Γ₄). The dielectric dispersion for E ⊥ c and E 6 c has been determined by Kramers-Kronig integrations.     

Ar-Broadening of isotropic Raman lines in the ν2 band of acetylene

Using a high resolution Raman spectrometer, we have measured Ar-broadening coefficients in the ν₂Q branch of C₂H₂ for 22 lines at 295 K, 20 lines at 174 K, and 16 lines at 134 K. These lines with J values ranging from 1 to 23 are located in the spectral range 1970.9-1974.3 cm⁻¹. The collisional widths are obtained by fitting each spectral line with a Rautian profile. The resulting broadening coefficients are compared with theoretical values arising from close coupling and coupled states calculations. A satisfactory agreement is obtained at room as well as at low temperatures, especially for odd J lines. By comparing broadening coefficients at 295, 174, and 134 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally, and theoretically.     

Infrared spectra of some matrix-isolated germanium,tin, and lead chalcogenides

Infrared spectra are reported for GeS, GeSe, GeTe, SnS, SnSe, PbS and PbSe in argon and nitrogen matrices at 12°K. The absorptions due to the matrix-isolated diatomic IV–VI molecules show considerable isotopic structure. The dimer absorptions are treated in terms of a D_2h planar model and indicate that the dimers have nearly square geometries and that the bond stretching force constants in the dimers are about half those of the diatomic molecules.     

Raman scattering from magnetic excitations in Cd1−xMnxTe semiconductor alloys

We have observed antisymmetric Raman scattering from low frequency magnetic excitations in Cd_1?xMn_xTe alloys with 0.1 ≤ × ≤ 0.7. Crystals with x = 0.65 and 0.7 exhibit a magnon line in the antiferromagnetic phase, centered at 10.5 and 12.0 cm^-1 respectively, at 5 K. The frequency and the intensity of these lines decrease markedly with increasing temperature, finally disappearing in the paramagnetic phase. Crystals with 0.4 ≤ × ≤ 0.6 exhibit a similar feature at 5 K over the frequency range 4.5 – 5.5 cm^-1. These are attributed to spin waves originating from antiferromagnetically ordered clusters within their spin-glass phase. All the alloys show a distinct inelastic wing in the paramagnetic phase, which may be related to the magnetic excitations within residual clusters of coupled Mn⁺⁺ spins.     

Temperature dependence of the lattice vibrations of triglycine selenate

The polarized Raman spectra below 300 cm^?1 and the far infrared spectra from 400 to 30 cm^?1 of triglycine selenate were measured at various low temperatures. It was found that the Raman doublet at 44 and 38 cm^-1 observed in the paraelectric phase (space group C²_2h) was reduced to a singlet at 38 cm^?1 in the ferroelectric phase (space group C₂²). This spectral anomaly in the paraelectric phase appears to be due to the splitting of the translational mode of glycine I along the crystallographic b axis, the splitting being caused by the tunneling of glycine I across the barrier between the two potential minima which are located symmetrically on either side of the crystallographic ac plane (i.e. at $\text{b =}\text{1}\text{4}$ and $\text{3}\text{4}\text{)}$. New Raman bands which appear below the Curie temperature are also discussed.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.     

Observation of a soft phonon in linear chain compound (NbSe4)3I by Raman scattering

The phase transition of the linear chain compound (NbSe₄)₃I was studied by Raman scattering. At 78 K three new peaks were observed at 73 cm^?1, 205 cm^?1 and 261 cm^?1. The totally symmetric Raman peak at 73 cm^?1 shows anomalous temperature dependence. The frequency decreases with increasing temperature, and at high temperatures an anticrossing occurs with another peak observed at about 58 cm^?1. The Raman intensity decreases and the linewidth broadens remarkably as the temperature increases. These properties allow us to assign this peak to a soft phonon. This fact indicates clearly the existence of a structural phase transition of a displacive type below room temperature.     

Investigation of the metastable state of Na2[Fe(CN)5NO] · 2H2O by optical spectroscopy I. Comparison of the Raman spectra of the ground and metastable state

When excited by the 514.5 nm radiation of an argon ion laser at temperatures below 150 K crystalline sodium nitroprusside Na₂[Fe(CN)₅NO] · 2H₂O can be transformed into an extremely long-living metastable state. The Raman spectra of the crystal in the metastable state and ground state are compared in the range of 50–2350 cm^-1. In the metastable state the ?(NO)-stretching vibration is shifted by more than 100 cm^-1 to smaller frequencies depending on the orientation of the sample with respect to the crystallographic axis. This indicates the population of the antibonding π¹(NO)-orbital. In addition two new vibrations appear at 566 and 422 cm^-1. The other vibrational frequencies of the molecular ion [Fe(CN)₅NO]^2- are scarcely shifted, but relative intensities change.     

Magnon Raman scattering in CoBr2

The one-magnon Raman spectrum of CoBr₂ has been investigated as a function of temperature, and peak frequency, integrated intensity and width parameters obtained. The results obtained for the band energy at low temperature (22.2 ± 0.2 cm^-1 at 5.7.K) are in good agreement with AFMR and neutron scattering results. The one-magnon energy renormalises relatively slowly with increasing temperature and is about 15 cm^-1 at T_N = 19 K, whereas the integrated intensity approaches zero like the magnetization at T_N and the width diverges. A low intensity band at 26.8 ± 1 cm^-1 (7.6K) may be due to two-magnon scattering from spin waves along the c-axis.     

Self-density frequency shift measurements of Raman N2 Q-branch transitions

We report stimulated Raman investigations of N₂ Q-branch transitions in view to measure the self-density frequency shift. These measurements performed at 295 K over the density range 0.02-0.8 Amagat lead to a mean shift value equal to -5.5×10^-3 cm^-1/Amagat. Moreover, our data extrapolated at zero density allowed new refinements of the N₂ molecular constants: v₀=2329.91165 (17) cm^-1, B₁–B₀=-0.0173714 (22) cm^-1 and D₁–D₀=(7.6±5.0)×10^-9 cm^-1.     

Molecular vibrations of isotope labelled TTF-TCNQ. evidence of electron-phonon interaction

The infrared (IR) and Raman (R) spectra of TTF-TCNQ, TTF-TCNQ-¹⁵N₄, TTF-²H₄-TCNQ, and TTF-TCNQ-²H₄ have been measured, with particular emphasis on the CN stretching vibrations. The lines at 2206 cm^-1 (IR) and 2214 cm^-1 (R) are assigned to modes of A_1g symmetry. The isotope shift of the IR lines are unusual. The data suggest strong coupling between the CN stretching vibrations and the electronic motions.     

Far infrared absorption of a-GeSe

Far infrared absorption measurements have been made on a series of a-Ge_xSe_1?x films with near equiatomic compositions. The only sharp feature is an absorption line at 260cm^-1, and the compositional dependance of this feature is correctly described by a model in which the Ge(Se) atoms are 4(2) fold co-ordinated. There is no evidence in our amorphous samples of any absorption band in the frequency range (160?190cm^?1) of the major IR active modes of 3:3 fold co-ordinated crystalline GeSe.     

Observation of electronic Raman transitions from the transition metal ions Ti3+ and V4+ highly diluted in α-Al2O3

α-Al₂O₃ : Ti³⁺ (300 mass ppm concentration) at 10 K shows two electronic Raman transitions at 38 cm^-1 and 109 cm^-1. The E symmetry of the scattering matrix agrees with the selection rules for transitions between the ground state B_{$\text{3}\text{2}$} and the E_{$\text{1}\text{2}$} of the ground state manifold ²t_2g.α-Al₂o₃ : V⁴⁺ shows two very weak electronic Raman transitions at about 30 cm^-1 and 56 cm^-1 respectively.     

Intensity measurements in the v4-fundamental of methane

The absolute intensities of all the J-multiplets between R(13) at 1375cm^-1 and P(12) at 1225 cm^-1, in the v₄-fundamental of ¹²CH₄, have been measured at 300°K. Our values are consistent with published band-intensity measurements and also with the theoretical line strength tabulation by Fox. Spectral transmittance computation using a Lorentz line shape with a hydrogen-broadened half-width of 0.075 cm^-1 atm^-1 at 300°K for all the lines in the band is in excellent agreement with our experimental data measured with a spectral resolution of 0.2 cm^-1. Our best estimate for the absolute intensity of the band is 145±8 cm^-2 atm^-1 at STP.