Effects of frequency change on vibronically induced resonance raman scattering

Frequency change effects on vibronically induced resonance Raman scattering (VIRRS) have been theoretically studied. It is shown that the excitation energy profile consists of a succession of doublets. The Raman spectrum of pyrazine resonant to the S₁ state has been calculated using the derived analytical expressions for the cross section.     

The pure rotational raman spectrum of pyrazine C4H4N2

The pure rotational Raman spectrum of pyrazine, C₄H₄N₂, has been observed for the first time. The spectrum was recorded photographically using a 3 m spectrograph with a reciprocal linear dispersion of 1.4 cm⁻¹ mm⁻¹. The following rotational constants were obtained:

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The quantum yields of fluorescence and intersystem crossing in pyrazine-h₄ and -d₄ and pyrimidine vapors have been studied at moderately high pressures (50–100 Torr) in the presence of a foreign gas as a function of excitation energy in the S₁ (n, π*) ← S_o absorption region. The fluorescence quantum yield of pyrazine fluctuates in the lower energy region, but on the average is constant over the range of the excess vibrational energy 0–4000 cm^?1, whereas the fluorescence yield of pyrimidine decreases smoothly with increasing excess energy. For each of the three molecules, the intersystem crossing yield is approximately constant with a value near unity in a wide range of the excess energy, indicating that the intramolecular nonradiative transition from S₁ is governed by the crossing to the triplet state. From a calculation based on the first-order vibronic coupling (Herzberg-Teller) theory the radiative rate constant of the pyrazine fluorescence is found to be relatively large for the vibronic levels involving a non-totally symmetric vibration, ν₁₀₂. This accounts for the fluctuation of the fluorescence yields of pyrazine-h₄ and -d₄.     

2,6-Bis(porphyrin)-substituted pyrazine: a new class of supramolecular synthon binding to a transition-metal ion and fullerene (C60)

2,6-Disubstituted-3,5-dimethylpyrazines have been synthesized via biased acetal synthesis from symmetric 2,3,5,6-tetrakis(chloromethyl)pyrazine. The pyrazine ligands coordinated to trans-dichloropalladium(II) at the nitrogen whose neighboring carbons were connected to less hindered methyl groups. 2,6-Bis(porphyrin)-substituted pyrazine bound C₆₀ to yield 1:1 inclusion complex. The binding of C₆₀ with the pyrazine ligand and its zinc complex was determined by ESI-MS, NMR, and fluorescence spectroscopic analyses.     

香豆素343敏化TiO2纳米粒子光致电子转移的荧光和拉曼光谱

通过对香豆素343(C343)染料敏化TiO₂纳米粒子光致电子转移的荧光和拉曼光谱特性的研究表明,C343染料敏化TiO₂纳米粒子稳态吸收光谱和稳态荧光光谱的红移归因于从被吸附的C343染料分子激发态和C343/TiO₂复合物到TiO₂纳米粒子导带的光致电子转移. 由时间分辨荧光光谱确定了C343染料敏化TiO₂纳米粒子的逆向电子转移速率常数为τ₁=31 ps. C343 染料敏化TiO₂纳米粒子体系拉曼光谱的研究表明, 被吸附在界面处的染料分子主链碳键的伸缩振动和碳环的呼吸运动的振动模式对超快界面光致电子转移有着重要的促进作用.     

Direct visual evidence for chemical mechanism of SERRS of pyrazine adsorbed on Ag nanoparticle via charge transfer

In this paper, the chemical enhancement of surface-enhanced resonance Raman scattering (SERRS) of pyrazine adsorbed on Ag nanoparticles through charge transfer was experimentally and theoretically investigated. Based on the calculations by density functional theory (DFT) and time-dependent DFT (TD-DFT), we theoretically analyzed the absorption spectra and SERS spectrum of the S-complex of pyrazine–Ag₂₀. The charge transfer in the process of resonant electronic transitions between adsorbed molecule and metal cluster can be visualized by the method of charge difference density. It is a direct evidence for the chemical enhancement mechanism of SERRS of pyrazine molecule adsorbed on Ag nanoparticle via charge transfer between molecule and metal. Additionally, the intracluster charge redistribution was also considered as an evidence for the electromagnetic enhancement. By comparing the experimental and theoretical results, it was demonstrated that the SERRS of the pyrazine molecule absorbed on silver clusters in different incident wavelength regions is dominated by different enhancement mechanisms via the chemical and electromagnetic enhancements.     

Herzberg-teller effect and intensity distribution in the absorption and raman scattering resonance spectra of polyatomic molecules

This paper studies the influence of the Herzberg-Teller effect on the intensity distribution in one- and two-photon absorption and Raman scattering resonance spectra of substituted benzenes. A quantum mechanical analysis of the intensity distribution in the spectra of phenylacetylene and pyrazine is accomplished using the general approach suggested in [1, 2]. Due to the inclusion of vibronic coupling in the calculation, one can explain the presence of lines (as well as their combinations and overtones) arising from one-quantum excitation of nontotally symmetric vibrations. The calculated data are in good agreement with the experimental data. Significantly, the two-photon absorption spectrum of pyrazine in the region of the¹A_1g→¹B_3u long-wave singlet-singlet transition is explained only by the Herzberg-Teller effect. Saratov State Pedagogical Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 304–309, March–April, 1995. Translated by L. Smolina     

IR and Raman Vibrational Assignments for Metal-free Phthalocyanine from Density Functional B3LYP／6-31G（d） Method

Vibrational (IR and Raman) spectra for the metal-free phthalocyanine (H2Pc) have been comparatively investigated through experimental and theoretical methods. The frequencies and intensities were calculated at density functional B3LYP level using the 6-3 IG(d) basis set. The calculated vibrational frequencies were scaled by the factor 0.9613 and compared with the experimental result. In the IR spectrum, the characteristic IR band at 1008.cm^-1 is interpreted as C-N (pyrrole) in-plane bending vibration, in contrast with the traditional assigned N-H in-plane or out-of-plane bending vibration. The band at 874 cm^-1 is attributed to the isoindole deformation and aza vibration. In the Raman spectrum, the bands at 540, 566, 1310, 1340, 1425, 1448 and 1618 cm^-1 are also re-interpreted. Assignments of vibrational bands in the IR and Raman spectra are given based on density functional calculations for the first time. The present work provides valuable information to the traditional empirical assignment and will be helpful for further investigation of the vibration spectra of phthalocyanine analogues and their metal complexes.     

Vibrational spectroscopic studies of three dimensional host lattices formed by pyrazine bridges between tetracyanonickelate layers

Three dimensional host lattices have been developed by forming bridges with bidentate pyrazine molecules between adjacent tetracyanonickelate polymeric layers of Ni(II) or Cd(II). The Fourier-transform IR and Raman spectra (4000-200 cm^–1) of the compounds with the general formula M(pyz)Ni(CN)₄, (where M = Ni or Cd) are reported. These host lattices can include benzene molecules but it is found that aniline molecules cannot be included in these structures. They, however, form complexes with the formula M(an)₂Ni(CN)₄, by replacing pyrazine ligands. A monodentate pyrazine complex of Cd(II) with the formula Cd(pyz)₂Ni(CN)₄ has also been prepared.     

Further evidence of the vibronic coupling of pyrazine as revealed by preresonance raman effect

The excitation wavelength dependences of the intensities of the Raman lines of pyrazine have been measured. The intensity enhancement of the non-totally symmetric Raman line at 925 cm^?1 provided firm evidence of the vibronic coupling between the lowest ¹B_3u(n,π^*) and second lowest ¹B_2u(π,π^*) states. The excitation wavelength dependences of other non-totally symmetric Raman lines suggest also the various vibronic coupling schemes.     

Syntheses,Structures, and Thermal Reactivity of New ZnII and CdII Thio‐ and Selenocyanato Coordination Compounds

Reaction of Zn^II and Cd^II thiocyanate or selenocyanate with pyrazine leads to the formation of new Zn^II and Cd^II coordination compounds. The structures of [Zn(NCSe)₂(pyrazine)₂]_n ( 1A ), [Cd(NCS)₂(pyrazine)₂]_n ( 2A ) and [Cd(NCSe)₂(pyrazine)₂]_n ( 3A ) consist of octahedrally coordinated metal cations which are surrounded by two terminal N‐bonded anions and two μ₂‐bridging pyrazine molecules. The metal cations are connected via the pyrazine ligands into layers, which are further linked by weak intermolecular S···S respectively Se···Se interactions. Investigations on the thermal degradation behavior of 1A , 2A , and 3A using simultaneous differential thermoanalysis and thermogravimetry as well as X‐ray powder diffraction, IR‐ and Raman spectroscopy prove that on heating, the pyrazine‐rich compound 1A decomposes in one step into zinc selenocyanate without the formation of a pyrazine‐deficient intermediate. In contrast, for compounds 2A and 3A a stepwise decomposition is observed, leading to the formation of the pyrazine‐deficient compounds [Cd(NCS)₂(pyrazine)]_n ( 2B‐I and 2B‐II ) and [Cd(NCSe)₂(pyrazine)]_n ( 3B ) as intermediates. The structures and the thermal reactivity are discussed and compared with that of related transition metal thiocyanates and selenocyanates with pyridine as N‐donor ligand.     

Direct observation of the twisting vibration in tetrachloroethylene through the hyper-Raman effect

The hyper-Raman spectrum of liquid C₂Cl₄ was recorded with Nd-YAG laser excitation and single channel detection. In addition to the known infrared active vibrations the Raman and infrared inactive twisting vibration ν₄(a_u) was observed at 106 ± 3 cm^?1.     

Influence of an identified dimer vibration on the emission spectrum of [2,2]paracyclophane

The emission spectrum of polycrystalline [2,2]paracylophane shows a resolved vibronic structure with a 241 cm^?1 progression at He temperatures. The dependence of the energy of this mode upon selective deuteration in combination with results from FIR and Raman spectra could be used to identify the mode as a torsional dimer vibration. The emission spectra could be simulated assuming a linear coupling of the torsional mode to the electronic transitions with coupling strengths of S = 10 (fluorescence) and S = 13 (phosphorescence). This corresponds to an equilibrium displacement of the benzene rings under electronic excitation by a torsional angle of 10.6° (S₁) and 12.1° (T₁), in addition to the small torsion in the ground state S₀ by about 3°.     

Ag(I) coordination polymer with pyrazine sulfonic acid: synthesis,crystal structure,and fluorescence property

A one-dimensional rigid, linear Ag(I) coordination polymer with pyrazine sulfonic acid, [Ag₂L₂?·?H₂O] _n (L?=?pyrazine sulfonic acid) has been synthesized and characterized by elemental analyses, infrared spectroscopy, thermogravimetric analysis, and X-ray crystallography. The structure determination shows Ag(I) centers linked by bridging pyrazine ligands to give a double-chain structure sustained by weak Ag-O and Ag-N interactions. The sulfonate and pyrazine are all involved in hydrogen bonding interaction. The interactions combine with weak π-π stacking to play deciding roles defining the supramolecular structures. A powder X-ray diffraction study implies good phase purity. Solid-state fluorescence quenching and thermal stability are also discussed.     

Infrared and Raman spectroscopic characterization of the phosphate mineral kosnarite KZr2(PO4)3 in comparison with other pegmatitic phosphates

In this research, we have used vibrational spectroscopy to study the phosphate mineral kosnarite KZr₂(PO₄)₃. Interest in this mineral rests with the ability of zirconium phosphates (ZP) to lock in radioactive elements. ZP have the capacity to concentrate and immobilize the actinide fraction of radioactive phases in homogeneous zirconium phosphate phases. The Raman spectrum of kosnarite is characterized by a very intense band at 1,026?cm^?1 assigned to the symmetric stretching vibration of the PO₄ ^3? ??₁ symmetric stretching vibration. The series of bands at 561, 595 and 638?cm^?1 are assigned to the ??₄ out-of-plane bending modes of the PO₄ ^3? units. The intense band at 437?cm^?1 with other bands of lower wavenumber at 387, 405 and 421?cm^?1 is assigned to the ??₂ in-plane bending modes of the PO₄ ^3? units. The number of bands in the antisymmetric stretching region supports the concept that the symmetry of the phosphate anion in the kosnarite structure is preserved. The width of the infrared spectral profile and its complexity in contrast to the well-resolved Raman spectrum show that the pegmatitic phosphates are better studied with Raman spectroscopy.     

Observation of photodissociation of S2Cl2 and resonance Raman and fluorescence spectra of S2Cl under 514.5 nm radiation

The laser Raman spectrum of S₂Cl₂ varies with the sample temperature and/or the laser power. The Raman signals of S₂Cl₂ decreases as the sample molecules within the laser beam are dissociated by absorbing 514.5 nm photons. Above 540 K and 2 W of laser power, new resonance Raman and fluorescence bands appear. These bands were all assigned to S₂Cl. The fluorescence bands could be classified into two transition systems. Only one of them had the ground electronic state X̃ as its lower state. For the other, the low lying first excited state à was suspected. The fundamental frequencies suggested for the three vibrational modes were 664, 196 and 450 cm⁻¹ for the X̃ state and 630, 249 and 554 cm⁻¹ for the à state respectively.     

Unique coordination of pyrazine in T[Ni(CN)4]·2pyz with T=Mn, Zn, Cd

The materials under study, T[Ni(CN)₄]·2pyz with T=Mn, Zn, Cd, were prepared by separation of T[Ni(CN)₄] layers in citrate aqueous solution to allow the intercalation of the pyrazine molecules. The obtained solids were characterized from chemical analyses, X-ray diffraction, infrared, Raman, thermogravimetry, UV-Vis, magnetic and adsorption data. Their crystal structure was solved from ab initio using direct methods and then refined by the Rietveld method. A unique coordination for pyrazine to metal centers at neighboring layers was observed. The pyrazine molecule is found forming a bridge between Ni and T atoms, quite different from the proposed structures for T=Fe, Ni where it remains coordinated to two T atoms to form a vertical pillar between neighboring layers. The coordination of pyrazine to both Ni and T atoms minimizes the material free volume and leads to form a hydrophobic framework. On heating the solids remain stable up to 140 °C. No CO₂ and H₂ adsorption was observed in the small free spaces of their frameworks.     

Coordination of cations in TiNb2O7 by Raman spectroscopy

The Raman spectrum of the compound TiNb₂O₇ prepared by a liquid mix technique was recorded at room temperature using the 530.98-nm line from a krypton-ion laser as exciter. The bands observed at 998 and 884 cm^?1 are assigned to the edge-shared and corner-shared NbO₆ octahedra, respectively. The relative intensities of these two bands are consistent with the structure of TiNb₂O₇ worked out by earlier investigators using X-ray and neutron diffraction. The strong band observed at 647 cm^?1 is assigned to the vibration of the TiO₆ octahedra. The octahedral coordination for both cations based on the results of the Raman spectrum measurements is in essential agreement with the available structural data for the compound TiNb₂O₇. The weak band observed at 840 cm^?1 is suggestive of the presence of NbO₄ tetrahedra in small concentrations in TiNb₂O₇.     

Hydrogen bonding and fermi resonance of n-propylamine. Comparison of the results from i.r. and Raman measurements

Infrared and Raman spectra of neat propylamine in the NH₂ stretching and deformation vibration regions are compared. For the symmetric stretching vibration in the two spectra, opposite intensity relations are found, from which the appearance of only one i.r. but two Raman bands of the vibration is understandable. The wavenumbers for the symmetric vibration and the deformation vibration overtone are lower in the i.r. than in reported polarized Raman spectra. The influence of the reduced data on the Fermi resonance analysis of ν_s and 2δ is discussed.     

Resonanzramanspektrum von matrixisoliertem Se3

Resonance Raman Spectrum of Matrixisolated Se₃ By the application of a double furnace it is possible to get a gas mixture of 90% Se₂ molecules and 10% Se atoms. By condensing this mixture in an inertgas matrix at 15 K followed by annealing to nearly 25 K we got Se₃ molecules by a matrix reaction In the resonance Raman spectrum of this molecule we observed 14 overtones of the symmetric stretching vibration. So we can calculate the following values of ω₁ an x₁₁ for ⁸⁰Se₃: 312.15 ± 0.2 cm^?1 and 0.53 ± 0.02 cm^?1. Using a mixture of 62% ⁷⁶Se and 38% ⁸²Se we got band structures in which the intensity of the bands and their frequency shift can only be explained by a bent Se₃ molecule (～115°). The value of the force constant f_r + f_rr is 310 ± 20 Nm^?1. — By a new construction it is possible to get the Raman and IR reflection spectrum of the same matrix.