Polarised IR and Raman spectra of non-centrosymmetric Na3Li(SeO4)2.6H2O crystal--a new Raman laser material

Polarised IR and Raman spectra of Na₃Li(SeO₄)₂·6H₂O single crystal have been recorded. Discussion of the results has been based on the factor group approach for the trigonal R3c (C_3v⁶) space group with Z = 2. The obtained results for the spontaneous Raman scattering have been used in the discussion of the stimulated Raman spectra of the material studied—a new Raman laser crystal.     

Time-resolved electronic Raman spectrum of terbium aluminum garnet excited with visible and UV laser sources

Excitation profiles for the intensities of electronic Raman transitions between crystal field components of the ⁷F₆ and ⁷F₅ manifolds of terbium aluminum garnet are recorded for excitation in the spectral region where absorption bands due to levels of the ⁵D₄ manifold occur. The intensities of the electronic transitions are not enhanced which is thought to be caused by the small values of electric dipole matrix elements of the resonating electronic states in comparison to the values of such elements to other intermediate states which occur in the expression for the scattering tensor. Fluorescence from the ⁵D₄ levels is induced and resonance fluorescence are time resolved with respect to the Raman transitions. We report electronic Raman transitions excited with the 308.0 nm line of an XeCl excimer laser. As opposed to excitation with visible laser sources, transitions are recorded which terminate on all the crystal field levels of the ⁷F_5…0 levels. In addition, fluorescence from ⁵D₃ to the ground state of terbium aluminum garnet is also observed.     

Polarized Raman spectra IX. Low Frequency Vibrations in Crystallne Trans-Stilbene

Raman spectrum of powdered crystalline trans-stilbene is recorded by a laser Raman spectrometer. The intensity of a low frequency skeleton bending vibration at 220 cm⁻¹ is observed to be very weak. Its Raman intensity, after corrected for the photocathode response and for the v⁴ scattering factor, agrees within 10% of the theoretically calculated value. It is therefore proved that the intensity of a Raman active vibration is proportional to the square of its vibrational frequency, if only one excited state is involved in the scattering process. Lattice vibrations in trans-stilbene crystal are also reported.     

Local Raman tensors in adenosine triphosphoric acid

A polarized laser (488.0 nm) Raman spectroscopic measurement has been made on a single crystal of a disodium salt of adenosine triphosphoric acid (Na₂ATP·3H₂O) by the use of a Raman microscope. The crystal belongs to an orthorhombic system of the space group P2₁2₁2₁, and has dimensions of 10, 100 and 100 μm along the crystallographic axes a, b and c, respectively. For each Raman band in the 300–1800 cm⁻¹ range, the scattering intensity ratio I _bb/I _cc of the bb and cc polarization components has been determined. For a few bands, the relative intensities of the bc components were also estimated. To augment the data, the depolarization ratio of each Raman band of ATP has also been determined for its acidic (pH = 2.42) H₂O and D₂O solutions. From these experimental results, the shapes and orientations of the Raman scattering tensors which are considered to be localized in the adenine-H⁺ portion and in the phosphate portion of the molecule have been derived.     

Raman study of prereactional transformations in calcium hydroxide crystals during a thermal treatment leading to dehydration

The Raman spectroscopy study of Ca(OH)₂ single crystals shows that important modifications take place in the crystal structure far below the dehydration temperature. In particular, an intense and broad background scattering and a broad band centered at ～1650 cm^?1 evolve in the Raman spectra.     

The Studies of the Resonance Raman Scattering and the Chemical Reactions Involved in the Gaseous Iodine Bromide Under Argon Ion Laser Light

The resonance Raman spectra of gaseous iodine bromide IBr have been studied with the excitation of various argon ion laser lines from 5017 to 4579Å. The fine structures of the fundamental and few overtones of IBr are also studied by various power of 4880Å laser line. The resonance Raman scattering is found to be strong as that of Br₂ and ICI. A new term “apparent spectroscopic temperature” is suggusted for the case of the resonance Raman scattering. The apparent spectroscopic temperatures measured in this cell show that the system is not in thermal equilibrium. Br₂ is the hottest and I₂ is the coldest. IBr is in the middle. Unfortunately, no chemical reaction enhanced phenomenon is found although there should be some chemical reactions occurring under the laser light. The initiating reaction is the photodissociation of the main component IBr which also has large absorptivity. Because of the non-crossing between the B³Π and the ¹Π states, the primary products of the photodissociation should be I and Br. The chemical reactions of I and Br with IBr follow. The reactions of I and IBr is endothermic but the reaction of Br with IBr is exothermic. Therefore vibrational hot Br₂ is produced and its apparent spectroscopic temperature should be higher. On the other hand, the apparent spectroscopic temperature of I₂ is lower.     

Vibrational spectra of sodium gadolinium tungstate NaGd(WO4)2 single crystals: Observation of spatial dispersion

Room temperature polarized Raman scattering and infrared reflectance spectra of a NaGd(WO₄)₂ single crystal have been measured. The IR spectra interpretation was aided by a Kramers-Krönig analysis, and fitted to the independent oscillator model. All 13 theoretically expected Raman-active bands have been identified and assigned, as well as 7 out of 8 expected IR active bands. Splitting of bands in both Raman and IR clearly indicates a lowering of the crystal symmetry due to occupation disorder in the 4a site, that randomly accommodates either an Na⁺ or a Gd³⁺ ion. The reflectance IR spectra reveal a spatial dispersion, namely a dependence of the transverse optical (TO) polariton frequencies, on the propagation direction in the crystal. The crystal vibrational modes are correlated to the internal modes of the tungstate group WO₄^2?, and to the internal modes of the molecular skeleton. A detailed correlation map of the symmetry analysis is presented.     

Determination of the spontaneous raman linewidth of CF4 by measurements of stimulated raman scattering in both transient and steady states

The spontaneous Raman linewith Δv of the v₁ mode of gaseous CF₄ is determined from 30 to 360 amagat by comparison of stimulated Raman scattering threshold intensity measurements performed with picosecond and nanosecond laser excitation. At high densities Δv = 0.20 cm^?1 is constant. A possible explanation of this effect is given in terms of collisional narrowing     

Resonance raman spectra and quantum yields of MoS42−

Resonance Raman scattering of MoS₄^2? was studied in aqueous solution by irradiating its strong 4700 Å absorption band with five different lines of an Ar⁺ laser. The vibrational structure of the resonance spectra is discussed. Cross sections and quantum yields for the total scattered radiation were determined using NO₃^? as an internal standard.     

IR and Raman studies,and DFT quantum chemical calculations of the vibrational levels for α-4-methylbenzophenone

Polarized IR and Raman spectra of the oriented α-4-methylbenzophenone (C₁₄H₁₂O) single crystal have been measured. The assignment of the vibrational modes has been performed on the basis of quantum chemical calculations. The B3LYP/6-31G(d,p) quantum model and PED contributions have been applied in the discussion of the results. The dichroic behavior of several lines is analyzed and discussed in their relation to the results of QCC calculations and factor group analysis. The stimulated Raman spectrum of the crystal studied has been recorded. It has been shown that the ν(CH)_ϕ symmetric A_g vibration at 3065 cm⁻¹ participates efficiently in the stimulated effect and it could be used as a promoting mode of a new laser Raman material based on the 4-methylbenzophenone crystal.     

Polariton splittings of deuterated hexamethylenetetramine

The i.r. absorption spectra and the Raman scattering spectra of polycrystalline deuterated hexamethylenetetramine (HMTD) have been recorded. The longitudinal and transverse components of all the i.r. active F₂ modes below 1200 cm⁻¹ are assigned in the Raman spectra (except ω₂₀). The observed polariton splittings have been used to determine the static dielectric constant (2.66 ± 0.035) which is the same as that for the HMT crystal. As expected, isotopic substitution does not change this macroscopic data.     

Resonance-enhanced Raman scattering by aggregated 2,2′-cyanine on colloidal silver

The Raman scattering spectrum of 2,2′-cyanine on colloidal silver metal particles is discussed. Preliminary assignments of some of the vibrational Raman bands to the motions of specific chromophoric units are presented and multiplet character of some bands is discussed. Enhanced Raman scattering of 2,2′-cyanine occurs when the laser radiation is tuned to the J-aggregate absorption feature at 575 nm. The enhancement in Raman intensity is the result of a diminution of fluorescence intensity, as well as a quantitative increase in Raman scattering intensity, and is distinct from other types of enhancement phenomena (e.g., resonance Raman of monomeric solution dye, and surface-enhanced Raman scattering (SERS)). The resonance Raman enhancement, due to excitation at the frequency corresponding to the J-aggregate absorption, is found to be 2 × 10⁺³.     

Structural investigation of (CuI)0.45–(Ag2WO4)0.55 solid electrolyte using X-ray photoelectron and laser Raman spectroscopies

X-ray photoelectron spectroscopy (XPS) and laser Raman scattering (LRS) techniques have been employed to investigate the structure of amorphous (CuI)_0.45–(Ag₂WO₄)_0.55 solid electrolyte sample. XPS results reveal the presence of both Cu⁺ and Cu²⁺ ions whereas tungsten is found to exist only in the oxidation state of +6. The deconvolution of the O 1s spectrum into non-bridging and bridging oxygen atoms in conjunction with the laser Raman analysis tend to show that the amorphous (CuI)_0.45–(Ag₂WO₄)_0.55 solid electrolyte sample is composed mostly of octahedral WO₆ units that probably form [W₄O₁₆]⁸⁻ tetramer clusters, the existence of which is unique in the case of oxyhalide glasses.     

Excited state electron transfer from photoexcited fac-CIRe(CO)3(2,2′-bipyridine) to N,N′-dimethyl-4,4′-bipyridinium detected by transient

Pulsed laser excitation of fac-CIRe(CO)₃(bpy) in CH₃CN containing N,N′-dimethyl-4,4′-bipyridinium, MV²⁺, results in excited state electron transfer to form MV⁺ that can be detected by the Raman scattering from the trailing portion of the 18 ns 354.7 nm pulse from the frequency-tripled Nd : YAG laser excitation source. Essentially the same results are found for the pulsed excitation of Ru(bpy)₃²⁺ in H₂O containing MV²⁺.     

Photon-echo decay of naphthalene in durene and perdeutero-naphthalene

Using two frequency-doubled, nitrogen laser pumped, dye-lasers we have measured the decay of the photon-echo in the lowest ¹B_1u ← ¹A_1g singlet state of naphthalene in durene and in perdeutero-naphthalene. Optical phase relaxation in the durene mixed crystal is believed to be caused by resonant phonon scattering in the ground and excited state, and in the isotopically mixed crystal by scattering of the excited state into the singlet exciton band. At the lowest achievable temperature (1.4 K), the photon-echo decay time (T₂) in both systems is still found to be much shorter than expected from the fluorescence decay times. Energy transfer is held responsible for this discrepancy.     

Micro-Raman Spectroscopy of Nanostructured Silver Sulfide

Nanostructured silver sulfide powder with an average particle size of about 45 nm, an acanthite α-Ag₂S monoclinic structure (space group P2₁/c), and nonstoichiometric composition Ag_1.93S has been synthesized by the chemical deposition method. The silver sulfide nanopowder has been studied by Raman spectroscopy. According to the Raman scattering data, heating the nanopowder with high-power laser radiation in air leads to photoinduced decomposition of the Ag_1.93S nanopowder to give silver metal. The Raman spectrum of the silver sulfide nanopowder shows a series of bands in the low-frequency range from 90 to 260 cm^–1 associated with vibrations of silver atoms, Ag–S bonds, and symmetric Ag–S–Ag longitudinal modes. Raman spectroscopy confirmed an acanthite monoclinic structure of synthesized silver sulfide nanopowder.     

Lithium isotope effects in the vibrational spectra of Li2SeO4

Polarized Raman scattering spectra have been measured in single crystal ⁷Li₂SeO₄ and ⁶Li₂SeO₄. Based on these data, symmetry-based band assignments are proposed for the ν₂, ν₄ and lithium mode regions. Vibrational coupling interactions are noted between the ν₂, ν₄ and the lithium translatory modes.     

Electronic Raman scattering from terbium gallium garnet excited with a picosecond laser

The electronic Raman (ER) spectrum of terbium gallium garnet, recorded using picosecond radiation from the frequency-doubled output of a Nd:YAG laser is reported. The observed spectral bands with frequency shifts up to 6000 cm−1 are the result of the effect of a strong crystal field which causes J-mixing between the ⁷F_6,5,....,0 states. The site symmetry of Tb³⁺ in the garnet can be confirmed from this spectroscopy.     

Ruby laser induced emission from NO2

Two different types of emission from excited NO₂ were observed using pulsed ruby laser light at 6943 Å. The first type of fluorescence was seen in the near-IR and results from the single photon excitation of NO₂ from the ground (²A₁) state. By observing the emission as a function of time an unexpected behavior was observed in the near IR and could be explained by a consecutive deactivation mechanism, wherein a secondary species is preferentially detected. A second type of emission recently observed in the blue spectral region is weaker and is due to a multiphoton process. The intensity of the blue emission is a function of the cube of the laser intensity at low pressures and approaches the square at high pressures. We attribute this variation to simultaneous deactivation of the NO₂^* intermediate by collision (square) and by anti-Stokes Raman scattering off of the NO₂^* (cube).     

二钼酸铵晶体饱和水溶液Raman光谱的变异现象及其机理

记录了常温下二钼酸铵晶体饱和水溶液的Raman光谱，并分别与二钼酸铵晶体、仲钼酸铵晶体、仲钼酸铵晶体饱和水溶液、水溶液状态下单钼酸根离子的Raman光谱进行了比较研究。结果表明：二钼酸铵晶体饱和水溶液Raman光谱相对二钼酸铵晶体Raman光谱，明显地发生了变异现象。二钼酸铵晶体饱和水溶液Raman光谱其主要特征峰最高振动频率937.6 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征峰最高振动频率937.6 cm^-1完全吻合，而其次高振动频率893.9 cm^-1，恰好介于水溶液中单钼酸根离子Raman光谱主要特征峰最高振动频率895.1 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征次高峰振动频率891.0 cm^-1之间，而且三者彼此接近。二钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值为2.1，与仲钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值4.4相比，一半不足。提出了一种利用Raman光谱主要特征峰振动频率及其主、次特征峰强度之比值对二钼酸铵晶体饱和水溶液组分同时进行定性和半定量分析的新方法。发现了常温下二钼酸铵晶体饱和水溶液中二钼酸根离子Mo₂O₇^2-已经不复存在，完全转变成了优势组分仲钼酸根离子Mo₇O₂₄^6-和次要组分单钼酸根离子MoO₄^2-；证明了常温下含钼水溶液酸化过程中溶液Raman光谱离散性变化现象的存在。运用结构化学和物理化学原理同时讨论了二钼酸铵晶体饱和水溶液Raman光谱发生变异现象的机理。