Spectra Of Pyrazine Research Articles

The theory of Surface Enhanced Hyper Raman Scattering (A review)

The Dipole Quadrupole theory of Surface Enhanced Hyper Raman Scattering (SEHRS), created by the authors is expounded in detail. Peculiarities of behavior of electromagnetic field on rough metal surfaces are considered. It is demonstrated that there is an enhancement of the dipole and quadrupole light-molecule interaction near the places of the surface with a large curvature. The expression for the SEHRS crosssection of symmetrical molecules is obtained. Selection rules for the scattering contributions are derived and a qualitative classification of the contributions after the enhancement degree is performed. Analysis of experimental spectra of pyrazine and phenazine, and also some another molecules is performed too. It is demonstrated a full coincidence of experimental regularities in these spectra with the theory suggested.

Enhanced Raman spectrum of pyrazine with the aid of resonant electron dynamics in a nearby cluster

Considerable enhancement of the electric dipole excitation in a pyrazine molecule is computationally demonstrated even under the nonresonant condition with the aid of resonant electron dynamics in a nearby linear Na4 cluster. A real-time and real-space electron dynamics simulation based on time-dependent density functional theory illustrates the details of the enhanced electric dipole excitation through analysis of the time-dependent dipole moment induced in the pyrazine molecule. Specific vibrational normal modes in the molecular plane of pyrazine are found to effectively couple with the photoinduced electronic oscillation of Na4.

Anharmonic resonances in the vibrational spectra of pyrazine

The quartic force field of pyrazine has been calculated in the B3LYP/6-31G(d) hybrid density-functional approximation. Based on the results of this calculation, the total IR (250–3800 cm−1) and Raman (400–3200 cm−1) spectra of pyrazine have been interpreted with consideration for the Fermi and Darling-Dennison resonances and their spectral manifestations. A precision method is proposed for anharmonic analysis of the vibrational states of polyatomic molecules on the basis of consideration of their theoretical anharmonicity constants in combination with the corresponding experimental frequencies. The method of linear scaling of frequencies has been theoretically substantiated.

Surface-enhanced hyper-Raman spectroscopy (SEHRS) and surface-enhanced Raman spectroscopy (SERS) studies of pyrazine and pyridine adsorbed on silver electrodes

Both surface-enhanced hyper-Raman spectroscopy (SEHRS) and surface-enhanced Raman spectroscopy (SERS) spectra of pyrazine and pyridine adsorbed on silver electrode surfaces were obtained at different potentials. Although there is a relaxation of the symmetry selection rule to a certain extent, it is demonstrated experimentally here that the SEHR spectrum for a centrosymmetric molecule (pyrazine) shows some new vibrational bands and significant relative intensity changes compared with its SER spectrum. By contrast, the SEHR spectrum for a non-centrosymmetric molecule (pyridine) resembles its SER spectrum and shows the absence of new vibrational bands. Our results also show that SEHRS is more sensitive to the interaction between the adsorbate and the substrate than SERS.

Electrochemical and Raman spectroscopic studies of pyrazine adsorption at the Au(210) electrode surface

Chronocoulometry and Raman spectroscopy have been applied to study pyrazine adsorption at the Au(210) electrode surface. The adsorption isotherms, Gibbs energies of adsorption, and the electrosorption valency for pyrazine adsorption at the Au(210) electrode surface have been determined. Surface-enhanced Raman Scattering (SERS) spectra of pyrazine adsorbed on an "unroughened" Au(210) electrode surface have been obtained for the first time. The thermodynamic data and the SERS spectra indicate that pyrazine adsorbs on the Au(210) electrode via the nitrogen lone pair (N-bonded configuration) over the whole range of electrode potentials investigated. Consequently, the pyrazine molecule assumes only the vertical orientation at this surface of gold. The adsorption of pyrazine at the Au(210) and Au(111) surfaces is compared and the influence of the surface crystallography on the adsorption of this molecule at gold electrodes is discussed. Keywords: adsorption at Au(210), pyrazine, SERS, chronocoulometry.

Surface-Enhanced Raman Spectra of Pyridine and Pyrazine Adsorbed on a Au(210) Single-Crystal Electrode

Surface-enhanced Raman scattering (SERS) spectra of pyrazine and pyridine adsorbed on an “unroughened” Au(210) electrode surface have been obtained for the first time. The SERS spectra indicate that both pyridine and pyrazine adsorb on the Au(210) electrode via their nitrogen lone pairs (end-on configuration). The integrated SERS intensities from the ring-breathing vibrations (ca. 1010 cm-1 for pyridine and 1019 cm-1 for pyrazine) were measured. The potential profiles (integrated SERS intensity versus potential plots) were compared to the surface coverage data, obtained electrochemically, for the adsorption of pyridine and pyrazine on Au(210). No simple relationship was found between the SERS intensities and the surface coverage data; however, it seems that the SERS intensities track the surface coverage for low surface concentrations (less than a monolayer).

15N NMR Spectra of Pyrazine, Methylpyrazines and TheirN-Oxides

15N NMR Spectra of Pyrazine, Methylpyrazines and TheirN-Oxides

The adsorption and orientation of pyrazine on silver electrodes: a surface enhanced Raman scattering study

Surface enhanced Raman scattering (SERS) spectra of pyrazine (pz) adsorbed on a silver electrode from aqueous solutions containing either 1.0 M KCl or 1.0 M KBr are presented. The SER spectra display bands which are usually forbidden in the normal Raman spectrum of pz. The presence of these forbidden bands and the orientation of the molecules on the electrode surface are discussed under the two most accepted surface enhancement theories: the charge transfer and the electromagnetic model. The dependence of SERS intensity of several pz vibrational modes on the applied potential (potential profile) is also presented for different pz concentrations and excitation wavelengths. SER spectra, obtained at potentials more negative than −900 mV (vs. SCE), contain new bands due to reduction of the pz molecule. It is clear that some of these products of decomposed pz remain trapped on the electrode surface, and this can lead to misunderstandings of the interpretation of the adsorbed pz spectrum. Several controversial aspects presented in the literature about the surface Raman spectrum of pz are clarified and discussed.

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 the1A1g→1B3u long-wave singlet-singlet transition is explained only by the Herzberg-Teller effect.

The adsorption of pyrazine, hydrogen sulfide and thiophene on copper: A quantum-chemical study

The bonding of pyrazine (C 4H 4N 2), hydrogen sulfide (H 2S) and thiophene (C 4H 4S) to copper surfaces has been examined employing semi-empirical MO-SCF calculations (INDO/S) and metal clusters of limited size (Cu n n = 14, 16, 17 and 18). The C 4H 4N 2Cu, H 2SCu and C 4H 4SCu adsorption bonds are mainly a product of the interaction of the 4s and 4p orbitals of the substrate with the LUMO and the sulfur or nitrogen lone pairs of the adsorbate. Based on these INDO/S results, the UPS spectra of pyrazine, H 2S and thiophene on copper surfaces are discussed and compared with experimental results. For each adsorbed molecule, charge transfers important to the change in work function are presented. The effects of chemisorption upon the CN, CC and CH bonds of pyrazine, the CS, CC and CH bonds of thiophene, and the SH bonds of H 2S are examined. The large reactivity of H 2S on copper surfaces is explained in terms of a thermochemical analysis.

ChemInform Abstract: The Analysis of Intensity Fluctuations for a Fully Resolved Spectrum: Pyrazine

Intensity fluctuations in the recently published fluorescence excitation spectrum of pyrazine in the 1B3u←1Ag 000 band are analyzed. A numerical study of a model Hamiltonian of a bright state coupled to a manifold of dark states is performed as an aid to the interpretation of the results. The distribution of fluctuations in the intensities computed for the model Hamiltonian is near to that expected in the chaotic limit.

Absorption Spectrum versus Excitation Spectrum of Pyrazine

AbstractThe first ME spectrum of pyrazine was measured as an excitation spectrum. Assuming the quantum yield to be constant over the spectrum it was considered as an absorption spectrum and de‐diagonalisation led to zero order energies and coupling constants of the singlet and triplet states. – By measuring the lifetimes of eight strong ME's we have now shown that the quantum yield varies by as much as a factor of three over the spectrum. With these lifetimes the excitation spectrum can be converted into a real absorption spectrum and a new and now correct set of values for the zero order energies, their widths and the coupling constants was obtained. The most important result is the fact that the zero order singlet and triplets decay non‐radiatively at different rates.

Multiphoton dissociation/ionization of benzene, pyridine, and diazabenzenes. Detection of an atomic carbon transition

Multiphoton processes in benzene, pyridine, and the diazabenzenes with ∼10 ns, 0.4–2.5 mJ pulsed laser light in the 336–347 nm range, produced resonantly enhanced molecular ions as well as neutral carbon atoms. The carbon atoms were detected by subsequent two-photon resonant (...2p2 1D2→2hν ...2p3p 1P1) three-photon ionization at 340.93 nm. MPI resonances due to vibrations of the 3p Rydberg state appeared in the spectra of pyrazine and pyrimidine, as well as a probable member of the first singlet→triplet band in pyrimidine.

Molecular aggregates in cryogenic solutions

Spectra of pyrazine, benzene, and osmium tetroxide have been obtained in cryogenic solutions. Data indicate that mixtures (∼ 10 ppm solute in solvent) deposited at low temperatures (∼ 100 K) yield clusters of solute molecules. The size of these clusters are estimated from light scattering data to be of the order of 103 Å. In particular, molecular aggregates appear in pyrazine/C3H8, benzene/NF3, CF4, OsO4/C3H8, NF3 but not in benzene/C3H8. The major factor governing the appearance of aggregates at low temperature is solubility. Upon warming these solutions to ∼150 K only solution spectra are observed; subsequent equilibrium cooling, of course, yields only precipitate.

Vibrational spectra of molecules on zeolites. Part 3.—Raman spectra of pyrazine on zeolites X

Laser Raman spectra of pyrazine on a series of alkali and alkaline earth cation exchanged X-type zeolites have been recorded. Within both the uni- and divalent cation series Raman line shifts on adsorption follow a direct cation polarizing power dependence. The observation that these line shifts are similar for zeolites incorporating uni- and divalent cations is in contrast with data for pyridine on similar surfaces. These differences between adsorbed pyrazine and pyridine have been interpreted in terms of the electronic properties of the former. For pyrazine on NaX, KX, CsX and MgX a line at ∼ 1154 cm–1 has been assigned to a CH bending mode which is Raman inactive for the free (D2h) molecule.

ChemInform Abstract: MEASUREMENT OF SINGLET‐TRIPLET ABSORPTION SPECTRUM OF PYRIDAZINE BY A SENSITIZED‐PHOSPHORESCENCE EXCITATION METHOD

The S0→T absorption spectrum of pyridazine was measured by means of sensitized-phosphorescence excitation in EPA rigid-glass solution at 77 K. Its intensity was found to be much lower than that of the corresponding spectrum of pyrazine.

Measurement of Singlet-Triplet Absorption Spectrum of Pyridazine by a Sensitized-Phosphorescence Excitation Method

Abstract The S0→T absorption spectrum of pyridazine was measured by means of sensitized-phosphorescence excitation in EPA rigid-glass solution at 77 K. Its intensity was found to be much lower than that of the corresponding spectrum of pyrazine.

ChemInform Abstract: ELECTRONIC SPECTRA AND VIBRONIC COUPLING OF PYRAZINE

Chemischer InformationsdienstVolume 5, Issue 41 Physical Organic Chemistry ChemInform Abstract: ELECTRONIC SPECTRA AND VIBRONIC COUPLING OF PYRAZINE ISAMU SUZUKA, ISAMU SUZUKASearch for more papers by this authorNAOHIKO MIKAMI, NAOHIKO MIKAMISearch for more papers by this authorMITSUO ITO, MITSUO ITOSearch for more papers by this author ISAMU SUZUKA, ISAMU SUZUKASearch for more papers by this authorNAOHIKO MIKAMI, NAOHIKO MIKAMISearch for more papers by this authorMITSUO ITO, MITSUO ITOSearch for more papers by this author First published: October 15, 1974 https://doi.org/10.1002/chin.197441072Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume5, Issue41October 15, 1974 RelatedInformation

Reversal in the sequence of the two highest occupied molecular orbitals in the series pyrazine, 2,6-dimethylpyrazine, and tetramethylpyrazine

Comparison between the photoelectron spectra of pyrazine (1), 2,6-dimethylpyrazine (2), and tetramethylpyrazine (3) indicates that in (3) the HOMO is π(b2g) while in (1) and (2) it is n+, suggesting a different behaviour towards electrophilic attack on (3) compared with (1) and (2).

Orientation and Structure of Pyrazine, Pyrimidine, and Pyridazine in a Lyotropic Liquid Crystal

Abstract High resolution proton magnetic resonance spectra of pyrazine, pyrimidine, and pyridazine partially oriented in a lyotropic mesophase have been obtained and analyzed. The distance ratios calculated from the direct dipole-dipole couplings are compared with those reported for microwave and X-ray studies in the gaseous and solid state as well as those determined from NMR investigations of the above solutes in thermotropic nematic phases. The average orientation of the diazines in the oriented lyotropic phase is such that the applied magnetic field is parallel to the molecular plane. In contrast, the average orientation of benzene, furan, thiophene, p-dithiin, and tetrafluoro-1,3-dithietane is such that the molecular ring is on the average perpendicular to the applied magnetic field. Sine benzene, furan, thiophene, and the diazines orient with the molecular plane parallel to the magnetic field in thermotropic nematic phases, contributions from different orienting factors appear to be operative in the...