Raman scattering in brominated (SN)x crystals

Detailed Raman scattering data on brominated (SN)_x crystals ranging in composition from (SNBr_0.27)_x to (SNBr_0.55)_x, and preliminary Raman data on [SN(ICI)_0.125]_x are discussed. The investigation involved a study under various conditions of temperature, pressure and levels of bromination, of the two primary Raman lines at 154 and 230 cm^-1 in brominated (SN)_x, which are polarized along the polymer axis direction. The analysis of the data is consistent with a model in which bromine enters the interfibrillar regions as Br^-₃ and the (SN)_x lattice as Br₂. Infrared data is also presented showing an appreciable decrease in intensity of the SN modes at 995 and 670 cm^-1 on bromination.     

Raman spectroscopy of SrB<Subscript>4</Subscript>O<Subscript>7</Subscript> single crystals in the temperature range 300–1273 K

The polarized Raman spectra of SrB₄O₇ (SBO) single crystals are studied in detail in the temperature range of 300–1273 K. The TO, LO, and IO phonon lines of A₁, A₂, B₁, and B₂ symmetries of rhombic SBO at 300 K are identified. The behavior of the Raman spectra of SBO crystals is studied upon heating up to their melting. The relation of Raman spectra with the structure of boron–oxygen fragments, as well as the transformation of spectra in the process of melting of SBO crystals, is discussed.     

Pressure dependence of the impurity soft modes in Li and Na : KTaO3

Low energy Raman scattering measurements on samples of K_0.76Na_0.24TaO₃, K_0.9Na_0.1TaO₃ and K_0.75Li_0.25TaO₃ under hydrostatic pressures of up to 60 kbar supply confirming evidence to the hypothesis that the Na⁺ ions in these crystals are displaced from the centers of the sites they occupy. The pressure Raman experiments also reveal another second order Raman line interpreted as Raman scattering by two TA phonons at M. A line induced by the substitution of Na for K is found to have an energy about equal to the energy of this new second order Raman line. It is shown that if this is a resonant mode it must be an even mode.     

Measurement of the quadratic Zeeman shift of Rb hyperfine sublevels using stimulated Raman transitions

We demonstrate a technique for directly measuring the quadratic Zeeman shift using stimulated Raman transitions. The quadratic Zeeman shift has been measured yielding Δν=1296.8±3.3 Hz/G² for magnetically insensitive sublevels (5S_1/2,F=2,m_F=0→5S_1/2,F=3,m_F=0) of ⁸⁵Rb by compensating the magnetic field and cancelling the ac Stark shift. We also measured the cancellation ratio of the differential ac Stark shift due to the imbalanced Raman beams by using two pairs of Raman beams (σ⁺, σ⁺) and it is 1:3.67 when the one-photon detuning is 1.5 GHz in the experiment.     

Raman scattering in stage 1 europium intercalated graphite

The Raman spectrum of stage 1 europium intercalated graphite, EuC₆, has been recorded at room temperature. EuC₆ has a p(√3 × √3)R30° in-plane superlattice structure, the same as that of LiC₆. The c-axis stacking sequences of EuC₆ and LiC₆ are different. The Raman spectrum of EuC₆ exhibits a broad asymmetric Fano resonance peak at 1500 ± 5 cm^-1, similar to that observed in MC₈ (M = K, RbandCs). However, there is no evidence of any spectral feature around 580 cm^-1 as what has been observed in MC₈. Considering the Raman features of various graphite intercalation compounds in light of their superlattice structures, we suggest that: (1) The feature around 580 cm^-1 is a characteristic associated only with the MC₈p(2 × 2)R0° in-plane superlattice structure. It should originate from the M point phonons of pristine graphite, which become Raman active as predicted by phonon band structure calculations. (2) The continuous background in the spectra of EuC₆ and MC₈, which results in the Fano resonance peak at 1500 cm^-1, is associated with the staggered stacking sequence. Stacking faults are easy to occur in crystals with staggered stacking sequences, but not in crystals with complete elliptical sequences. Therefore, a disorder induced continuum is observed in the Raman spectra of EuC₆ and MC₈, but not in that of LiC₆.     

Raman spectra of TiO2-II,TiO2-III,SnO2, and GeO2 at high pressure

Raman spectra of the orthorhombic (II) and high pressure (III) phases of titanium dioxide at pressures to 372 kbar and effects of temperature and hydrostatic pressure on Raman spectra of the tetagonal cassiterite-like phases of TiO₂, GeO₂ and SnO₂ are described. At room temperature, the TiO₂ II–III transition is sluggish, and metastable coexistence was observed from 200 to 300 kbar. The Raman spectra of TiO₂-III imply that its primitive cell contains at least four formula units; however, the structure could not be established from the Raman spectra and available powder X-ray diffraction patterns.The temperature and pressure dependences of the spectrum of the tetragonal MO₂ phases together with bulk moduli and thermal expansion data were used to evaluate the pure-volume and pure-temperature contributions to the isobaric temperature dependence of the Raman frequencies. Large anharmonicities in TiO₂ are attributed to hybridization of the oxygen p states with the d states of the Ti ion. GeO₂, where p-electron bonding is involved, is much less Enharmonic.     

Raman scattering of NiS2

Raman scattering measurements of NiS₂ is done and five optical phonon peaks are found. These peaks are assigned to A_g, E_g and 3T_g phonons which are all of the Raman active optical phonons in pyrite-type crystal. The results are compared with those of FeS₂ and MnS₂.     

Chemical composition of matrix-embedded ternary II–VI nanocrystals derived from first- and second-order Raman spectra

A one- and multiphonon Raman scattering study is performed for an extensive set of CdS_1–xSe_x, Cd_1–yZn_yS, Cd_1–yZn_ySe, and CdSe_1–xTe_x nanocrystals to investigate the applicability of first- and second-order Raman spectra for the determination of the matrix-embedded ternary nanocrystal composition. For one-mode ternary systems both the LO and 2LO phonon frequencies in the Raman spectra are shown to be a good measure of the nanocrystal composition. For two-mode systems, the approaches based on the difference of the LO phonon frequencies (first-order Raman spectra) or double LO overtone and combination tone frequencies (second-order Raman spectra) as well as on the LO phonon band intensity ratios are analysed. The weak electron–phonon coupling in the II–VI nanocrystals and the polaron constant values for the nanocrystal sublattices are discussed.     

Laser excited Raman spectra of Gr. VI semiconducting compounds

Raman spectra of hexagonal layer compounds MoS₂, MoSe₂ and MoTe₂ were excited by a HeNe laser (6328Å). All the Raman active long-wave-length phonon frequencies were determined. These are A_1g, E¹_2g, E_1g and E²_g. The frequencies decrease as we pass from sulphur to tellurium and the quasiacoustical mode E²_2g has the lowest frequency. A comparison of the results with infrared spectra shows that the i.r. active mode for E ⊥ C is degenerate with one of the Raman active modes in the basal plane for all the compounds.     

Raman spectroscopy of crystalline,glassy, and molten states of lead diborate

Polarized Raman spectra of single crystals of lead diborate, PbB₄O₇ (PBO), are studied in detail at 300 K. The TO-, LO-, and IO-phonon lines of the A ₁, A ₂, B ₁, and B ₂ symmetries in the Raman spectra of this compound are assigned. Changes in the Raman spectra of the internal vibrations of boron–oxygen complexes upon transition from the crystalline to the glassy and the molten states of PBO are observed. On the basis of the obtained results, the regularities in the formation of boron–oxygen complexes in glasses, melts, and crystals of the PbO · 2B₂O₃, SrO · 2B₂O₃, and Li₂O · 2B₂O₃. diborate compositions are analyzed.     

The ν5 and ν3 Raman bands of CH2D2

The ν₅ and ν₃ Raman bands of CH₂D₂ have been recorded with a resolution of 0.35 cm^?1. The ν₃ state is well known from infrared studies. Three hundred twenty-nine transitions of the ν₅ band were analyzed, assuming an unperturbed upper state, giving a standard deviation on the fit of the upper-state energies of 0.037 cm^?1, The constants A, B, C, Δ_J, Δ_JK, and Δ_K differed significantly from the ground-state values, and ν₅ was determined as 1331.41 ± 0.05 cm^?1. This work represents the first complete analysis of the fine structure of a rotation-vibrational Raman band for an asymmetric rotor. The ν₅ state could not be analyzed in infrared so this investigation, once more, demonstrates the usefulness of the Raman method.     

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.     

Determination of A0 of CH3Br from its Raman spectrum

A value of A₀ = 5.1800 ± 0.0010 cm^?1 for CH₃Br has been determined from an analysis of the ν₄ Raman band, based both on a direct fit of Q-branch frequencies and on ground state combination differences. The constants ν₄, (Aζ)₄, η₄₄, and A_e = 5.2442 ± 0.0015 cm^?1 were also determined. The equilibrium distance of the H atoms from the figure axis is calculated as 0.32077 ± 0.00005 Å. All the fundamental Raman bands of CH₃Br were observed, and experimental results for the ν₁, ν₂ and ν₅ bands are included.     

The effect of pressure on the Raman spectra of solids—IV. KSbF6 And CsSbF6

KSbF₆ has a tetragonal structure above 300 K, below 300 K. it is cubic and undergoes a phase transition at ∼ 3 kbar to a phase which is shown to be isostructural with that of rhombohedral CsSbF₆. Conclusive evidence is found in the polarized Raman spectra of single crystals of rhombohedral CsSbF₆ that they belong to the space group R3&#x0304;-C²_3i. The high-pressure Raman spectra of rhombohedral KSbF₆, TlSbF₆, and CsSbF₆ are compared and cationic effects are discussed.     

Vibrational spectra of M3PCr4O16 (M = K,NH4)

The infrared and Raman spectra of the two phosphochromates M₃PCr₄O₁₆ (M = K, NH₄) have been recorded and analysed. The spectra could be interpreted on the basis of the vibrations of Cr-O-P, O-P-O and CrO₃ groups. A large number of vibrational bands have been observed for each mode due to the existence of different Cr-O bond lengths. The anion is more distorted in potassium phosphochromate. The three ammonium groups are distinct.     

Comparison of the sensitivities of IR absorption and raman scattering spectra to hydrogen bonding in methanol

The sensitivity of infrared (IR) absorption and Raman scattering (RS) spectra to hydrogen bonding in methanol is quantified by a comparative sensitivity factor, which can be expressed as the K = (I _b /I _ub )_IR/(I _b /I _ub )_RS, where the indices b and ub refer to H-bonded and unbound (free) OH groups, respectively. The resulting value for methanol, K ～ 20, is identical to that found previously for n-butanol, although the methods of measuring the degree of hydrogen bonding for these two alcohols were quite different. It is shown that, in some cases, Raman spectra can be converted to IR absorption spectra and vice versa. It is important for understanding differences in the shapes of OH stretching vibration bands in IR absorption and Raman spectra.     

High-resolution inverse Raman spectroscopy of the ν1 band of 28SiH4

A near-Doppler-limited isotropic Raman spectrum of the symmetric stretching fundamental ν₁ of ²⁸SiH₄ has been recorded between 2182.8 and 2187.0 cm^?1 using high-sensitivity “quasi-cw” inverse Raman spectroscopy. The band exhibits compact, nonoverlapping J manifolds, which were measured from Q(0) through Q(13), plus a portion of Q(14). Since ν₁ is in resonance with the nearby infrared-active stretch ν₃, these two bands were analyzed simultaneously using the infrared frequencies of ν₃ reported by Cabana, Gray, Robiette, and Pierre. The results confirm their analysis, in which several perturbation-allowed ν₁ transitions were identified in the infrared, but the molecular constants for the v₁ = 1 state are much better determined with the inclusion of the Raman data. At higher J, ν₁ exhibits significant intensity perturbations due to a breakdown of the selection rule ΔN = 0; these have been quantitatively accounted for.     

The nature of the vibronic coupling in a metalloporphyrin and its Raman scattering

It has been shown that a Raman line of a nontotally symmetric vibration (b_1g, b_2g, or a_2g) of a metalloporphyrin (D_4h) can be caused, not only by a vibronic coupling between the first ($\text{A}\text{?}$) and second ($\text{B}\text{?}$) excited electronic states but also by a vibronic coupling within one of the electronic states (let us call the former the QS mechanism and the latter the QQ and/or SS mechanism). A simple formulation has been made for each of those different mechanisms, so that a numerical calculation can be made of the excitation profile of a Raman scattering for a given set of coupling constants and damping factors. Next, the result of an examination is given of the excitation profile of the Raman scatterings of some of the b_1g, b_2g, and a_2g vibrations of nickel octaethylporphyrin and nickel octaethyltetrachloroporphryin. Most of the Raman lines of these nontotally symmetric vibrations show a resonance effect only in the Q-band ($\text{A}\text{?}\text{←}\text{X}\text{?}$) region but not in the Soret-band ($\text{B}\text{?}\text{←}\text{X}\text{?}$) region. On the basis of this fact, it has been suggested that those Raman lines are caused mainly by the QQ mechanism rather than the QS mechanism. The observed vibrational structure of an excitation profile also seems to support this suggestion.     

Isotope effect in resonant Raman scattering and induced IR spectra of trans-polyacetylene

We present a full explanation of the isotope effect in resonant Raman scattering, doping induced, and photo-induced IR-active vibrations of previously reported data in trans-(CH)_x, (¹³CH)_x and (CD)_x. The interpretation is given in terms of Raman scattering from amplitude modes of the dimerized chains and absorption by charged induced IR-active modes. It is shown that the bare phonon frequencies are properly modified by the isotope mass whereas the observed frequencies are derived by the dressed phonon propagator, and therefore do not follow the usual mass rule.