Vibrational circular dichroism spectroscopy of a spin-triplet bis-(biuretato) cobaltate(III) coordination compound with low-lying electronic transitions

Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy was applied in the analysis of vibrational and low lying electronic transitions of a triplet ground state cobalt(III) coordination compound. The spectroscopic measurements were performed on the tetrabutylammonium salt of (6S,7S)-1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyl-dodecanato(4-)cobaltate(III) in DMSO solution and in potassium bromide pellets. The chiral anion exhibits an unusual geometry for cobalt(III), being four-coordinate, planar, and paramagnetic with an intermediate spin state. The spectroscopic results were compared to measurements performed on the free ligand and to theoretical calculations using density functional theory (B3LYP/TZVP). The results of the VCD analysis of the coordination compound identified an electronic, dipole-forbidden, magnetic dipole-allowed low-lying d-d transition located in the mid infrared, as well as several amide stretch transitions located in the fingerprint region (1800-1100 cm(-1)), in both the liquid and solid phase. VCD signals were found to be 5-10 times higher than expected, indicating enhancement of the vibrational CD signals, caused by coupling of the vibrational transitions with the close-lying electronic transition.     

Spectroscopic (NMR, UV, FT-IR and FT-Raman) analysis and theoretical investigation of nicotinamide N-oxide with density functional theory

The spectroscopic properties of the nicotinamide N-oxide (abbreviated as NANO, C(6)H(6)N(2)O(2)) were examined by FT-IR, FT-Raman, NMR and UV techniques. FT-IR and FT-Raman spectra in solid state were observed in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The (1)H and (13)C NMR spectra were recorded in DMSO. The UV absorption spectrum of the compound that dissolved in water was recorded in the range of 200-800 nm. The structural and spectroscopic data of the molecule in the ground state were calculated by using Density Functional Theory (DFT) employing B3LYP methods with the 6-311++G(d,p) basis set. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. The optimized structure of compound was interpreted and compared with the reported experimental values. The observed vibrational wavenumbers, absorption wavelengths and chemical shifts were compared with calculated values. As a result, the optimized geometry and calculated spectroscopic data show a good agreement with the experimental results.     

Experimental and theoretical studies on the identification of p-biphenyloxycarbonylphenyl acrylate

This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate by means of experimental and theoretical evidences. The spectroscopic properties of the compound were experimentally investigated by Fourier transformation-infrared spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). Moreover, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, thermodynamic properties, atomic charges and ultraviolet-visible (UV-vis) spectra were analyzed utilizing ab initio Hartree-Fock (HF) and Density Functional Theory (B3LYP) methods at 6-31G(d,p) calculation level. It was found that the vibrational frequencies and chemical shifts obtained were shown to have a good agreement with available experimental results. We not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also evaluated the transition state and energy band gap clearly.     

卤化氢共振增强多光子电离光谱

测定了卤化氢(HCl, HBr 和HI) (2+1)共振增强多光子电离(REMPI)光谱, 采用模拟计算法分析推导出转动常数、谱带源以及Ω态振动谱带的同位素位移值. 得到的HCl数据同Green等人用常规分析法所推导的结果极为吻合. 得出8条振动谱带,其中包括V(¹∑⁺)态, E(¹∑⁺)的v'=4态以及HBr的5个新谱带, 此外还推导出HI的E态v'=1的4个振动谱带光谱参数. 观测了V和E态之间因同类相互作用而产生的不规则能级间距、转动参数和同位素位移. 讨论了HCl和HBr的E态和V态振动谱带中的转动谱线序列O和S对Q的强度比变化,提出了双光子激发机理.     

Molecular structure and vibrational spectra of phenolphthalein and its dianion

Infrared (IR) and Raman spectra of phenolphthalein (PP) and its dianion form (sodium and potassium salts) were studied both in the solid state and in aqueous solution. Band assignments were carried out on the basis of the isotope shifts of the ring deuterated and 13C-substituted derivatives. Spectral analyses reveal that the PP dianion exists as mixtures of the benzenoid form (colorless) and the quinonoid form (colored) in the solid state and in aqueous solution, while the neutral PP solely takes the gamma-lactone form. This work provides the first vibrational spectroscopic evidence for the coexistence of the two species in the PP dianions.     

Vibrational spectra of palladium 5-nitrofuryl thiosemicarbazone complexes: experimental and theoretical study

The vibrational spectroscopic behavior of a series of 16 palladium(II) complexes with 8 bioactive nitrofuran containing thiosemicarbazones as ligands has been studied in the solid state. The IR and Raman spectra of these complexes and the free nitrofuran thiosemicarbazone ligands were recorded and analyzed. Experimental spectra were satisfactorily described by density functional theory (DFT) calculations. The combination of experimental and theoretical methods allowed us to perform the characterization of the main vibrations that show the mode of coordination of the thiosemicarbazone moiety to palladium even though these vibration bands are located in spectral regions showing a complicated pattern due to the presence of vibrations of the nitrofuran moiety and combination modes involving furan vibrations. A characteristic vibrational spectroscopic pattern has been defined for Pd(II) 5-nitrofuryl thiosemicarbazone complexes. This systematic knowledge may be useful for the analysis of the spectroscopic behavior of other coordination compounds holding the 5-nitrofuran thiosemicarbazone moiety.     

Molecular structure, vibrational spectral studies of pyrazole and 3,5-dimethyl pyrazole based on density functional calculations

In this work, the experimental and theoretical vibrational spectra of pyrazole (PZ) and 3,5-dimethyl pyrazole (DMP) have been studied. FTIR and FT-Raman spectra of the title compounds in the solid phase are recorded in the region 4000-400 cm(-1) and 4000-50 cm(-1), respectively. The structural and spectroscopic data of the molecules in the ground state are calculated using density functional methods (B3LYP) with 6-311+G** basis set. The vibrational frequencies are calculated and scaled values are compared with experimental FTIR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete vibrational assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SM) method. 13C and 1H NMR chemical shifts results are compared with the experimental values.     

Structural elucidation for triorganotin derivatives of 3-amino, 4-amino and 3,5-diaminobenzoate. Crystal structures of triphenyltin 4-aminobenzoate and trimethyl and triphenyltin 3,5-diaminobenzoate

Synthesis and structural investigation of trimethyl and triphenyltin esters of the 3-, 4-amino and 3,5-diaminobenzoic acids are reported as a reinvestigation of their local and overall molecular structure based on crystal structure determinations and on correlation of solid state vibrational and γ-emission spectroscopic evidence. Evidence is provided for the existence of more than one tin environment and therefore different carboxylate coordination modes in the compounds.     

Resonance Raman and density functional study of the excited state structural dynamics of 3-amino-2-cyclohexen-1-one in water and acetonitrile solvents

FT-Raman and/or FT-IR spectra of 3-amino-2-cyclohexen-1-one (ACyO) in solid state and/or in solvents of water and acetonitrile were obtained. Density functional theory calculations were done to help elucidate the vibrational band assignments. The A-band resonance Raman spectra of ACyO were acquired in water and acetonitrile solvents to examine the excited state structural dynamics and the state-mixing or curve-crossing tuned by solvents. A preliminary resonance Raman intensity analysis using the time-dependent wave-packet theory and simple model was done for ACyO in acetonitrile solvent. Resonance Raman spectroscopic probing of the excited state curve-crossing or state-mixing was proposed.     

Reduced dimension discrete variable representation study of cis-trans isomerization in the S1 state of C2H2

Isomerization between the cis and trans conformers of the S(1) state of acetylene is studied using a reduced dimension discrete variable representation (DVR) calculation. Existing DVR techniques are combined with a high accuracy potential energy surface and a kinetic energy operator derived from FG theory to yield an effective but simple Hamiltonian for treating large amplitude motions. The spectroscopic signatures of the S(1) isomerization are discussed, with emphasis on the vibrational aspects. The presence of a low barrier to isomerization causes distortion of the trans vibrational level structure and the appearance of nominally electronically forbidden A? (1)A(2)←X? (1)Σ(g)(+) transitions to vibrational levels of the cis conformer. Both of these effects are modeled in agreement with experimental results, and the underlying mechanisms of tunneling and state mixing are elucidated by use of the calculated vibrational wavefunctions.     

Ab initio configuration-interaction study of the ground and low-lying electronic states of NiI

For the first time, we have studied the potential-energy curves, spectroscopic terms, vibrational levels, and the spectroscopic constants of the ground and low-lying excited states of NiI by employing the complete active space self-consistent-field method with relativistic effective core potentials followed by multireference configuration-interaction calculations. We have identified six low-lying electronic states of NiI with doublet spin multiplicities, including three states of Delta symmetry and three states of Pi symmetry of the molecule within 15 000 cm(-1). The lowest (2)Delta state is identified as the ground state of NiI, and the lowest (2)Pi state is found at 2174.56 cm(-1) above it. These results fully support the previous conclusion of the observed spectra although our computational energy separation of the two states is obviously larger than that of the experimental values. The present calculations show that the low-lying excited states [13.9] (2)Pi and [14.6] (2)Delta are 3 (2)Pi and 3 (2)Delta electronic states of NiI, respectively. Our computed spectroscopic terms, vibrational levels, and spectroscopic constants for them are in good agreement with the experimental data available at present. In the present work we have not only suggested assignments for the observed states but also computed more electronic states that are yet to be observed experimentally.     

Novel polysilsesquioxane-I-/I3- ionic electrolyte for dye-sensitized photoelectrochemical cells

A new sol-gel precursor, based on 1-methyl-3-[3-(trimethoxy-lambda(4)-silyl)propyl]imidazolium iodide (MTMSPI(+)I(-)), was synthesized and investigated as a potential novel quasi-solid-state ionic liquid redox electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of the Graetzel type. MTMSPI(+)I(-) was hydrolyzed with acidified water, and the reaction products of the sol-gel condensation reactions were assessed with the help of (29)Si NMR and infrared spectroscopic techniques. Results of time-dependent analyses showed the formation of a positively charged polyhedral cubelike silsesquioxane species, which still contained a small amount of silanol end groups that were removed after heating at 200 degrees C. After cooling, the material formed was a tough, yellowish, and transparent solid, consisting mainly of ladderlike polysilsesquioxane species. The specific conductivity (sigma) of the nonhydrolyzed MTMSPI(+)I(-) (no I(2)) was 0.23 mS/cm, while the activation energy (E(a)), determined from the Vogel-Tamman-Fulcher (VTF) relation, was 0.29 kJ/mol. After 56 days of aging the sigma value of the hydrolyzed MTMSPI(+)I(-) dropped to 0.11 mS/cm but the viscosity had already increased to 7500 Pa.s after 17 days, demonstrating that a quasi solid state was attained. Apparent diffusion coefficients (D(app)) of I(-) and I(3)(-) obtained from the voltammetric measurements were approximately 10(-7) cm(2)/s and decreased to approximately 10(-8) cm(2)/s after 15 days of sol aging. Time-dependent vibrational spectra, which served in assessing the hydrolysis and condensation reactions of MTMSPI(+)I(-), were measured with the help of the attenuated total reflectance (ATR) IR spectroscopic technique. The results revealed that, in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to a shift of the vibrational band position in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined, and the results are applied in this work.     

FT-IR, UV-vis, 1H and 13C NMR spectra and the equilibrium structure of organic dye molecule disperse red 1 acrylate: a combined experimental and theoretical analysis

This study reports the characterization of disperse red 1 acrylate compound by spectral techniques and quantum chemical calculations. The spectroscopic properties were analyzed by FT-IR, UV-vis, (1)H NMR and (13)C NMR techniques. FT-IR spectrum in solid state was recorded in the region 4000-400 cm(-1). The UV-vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of 200-800 nm. The (1)H and (13)C NMR spectra were recorded in CDCl(3) solution. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR spectrum. A satisfactory consistency between the experimental and theoretical spectra was obtained and it shows that the hybrid DFT method is very useful in predicting accurate vibrational structure, especially for high-frequency region. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties were performed by timedependent DFT (TD-DFT) and CIS(D) approach. To investigate non linear optical properties, the electric dipole moment μ, polarizability α, anisotropy of polarizability Δα and molecular first hyperpolarizability β were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials.     

Experimental and computational studies of the structure and vibrational spectra of pyridinium-betaine of squaric acid

The FTIR spectra of pyridinium-betaine of squaric acid in 4000-100 cm(-1) frequency region in solid state were measured. In addition, the structure and harmonic vibrational frequencies of this molecule were theoretically evaluated using restricted Hartree-Fock and B3LYP density functional methods. The computed vibrational frequencies are used to determine the types of molecular motions associated with each of the experimental bands observed. Comparison with the experimental spectra provides important information about the ability of these computational methods to describe the vibrational modes in these highly polar strained ring compounds.     

Vibrational spectra, tautomerism and thermodynamics of anticarcinogenic drug: 5-fluorouracil

The FT-IR and FT-Raman spectra of 5-Fluorouracil were recorded in the solid phase in the regions 400-4000 cm(-1) and 50-4000 cm(-1), respectively. The vibrational spectra were analysed and the observed fundamentals were assigned to different normal modes of vibration. The experimental wavenumbers were compared with the scaled vibrational values using DFT methods: the Ar matrix data were related to gas phase calculations, while the values of the solid state spectra were compared to those with dimer simulations. The study indicates that some features that are characteristic of vibrational spectra of uracil and its derivatives are retained in the spectrum of 5-fluorouracil and it exists in ketonic form in the solid phase. The tautomerism was also studied and the spectra of the two most stable forms were simulated. The calculated wavenumbers have been employed to yield thermodynamic properties.     

2-Benzyl-2-methyl-2H-benzimidazole 1,3-dioxide derivatives: Spectroscopic and theoretical study

The spectroscopic behavior of 2-benzyl-2-methyl-2H-benzimidazole 1,3-dioxide derivatives in solution was studied in terms of electronic and nuclear magnetic resonance ((1)H and (13)C NMR) techniques. The experimental spectra were compared to the theoretical ones, obtained at DFT level, proving that the compounds adopt in solution a bird-like conformational distribution. Also, theoretically this conformational distribution resulted the most stable in gas phase. Infrared spectroscopy was used to study solid state behavior identifying experimentally the N-O stretching near to 1380, 1365 and 1225 cm(-1) and the vibrational benzimidazole skeleton near to 1610 and 1590 cm(-1). The vibrational spectrum was satisfactorily described by DFT calculations funding the N-O stretching as a coupled vibration near to 1470, 1350 and 1285 cm(-1). The fragmentation that takes place in mass spectrometry was assigned for all of the new derivatives.     

Photodissociation spectroscopy of stored CH+ and CD+ ions: analysis of the b 3Sigma(-)-a 3Pi system

We have measured the photodissociation spectrum of CH(+) and CD(+) molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b (3)Sigma(-)-a (3)Pi bands were observed as strong resonances because a large fraction of the ions in the metastable a (3)Pi(v=0) state were pumped to b (3)Sigma(-) levels and predissociated via the c (3)Sigma(+) state into C(+) and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH(+) and the 3-0 and 4-0 bands in CD(+), we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH(+). Combining all data delivers new, significantly adjusted equilibrium constants for the b (3)Sigma(-) and a (3)Pi electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b (3)Sigma(-) vibrational levels in CH(+) and compare them to a model. For the initial rovibrational distribution of the stored metastable CH(+) molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X (1)Sigma(+) ground state. New aspects of the spin-forbidden a (3)Pi-X (1)Sigma(+) radiative decay are discussed. Finally, we predict b (3)Sigma(-)-a (3)Pi absorption and a (3)Pi-X (1)Sigma(+) emission lines through which CH(+) in the metastable a (3)Pi(v=0) state might be detectable in astrophysical environments.     

Spectroscopy of highly excited vibrational states of HCN in its ground electronic state

An experimental technique based on a scheme of vibrationally mediated photodissociation has been developed and applied to the spectroscopic study of highly excited vibrational states in HCN, with energies between 29,000 and 30,000 cm(-1). The technique consists of four sequential steps: in the first one, a high power laser is used to vibrationally excite the sample to an intermediate state, typically (0,0,4), the nu3 mode being approximately equivalent to the C-H stretching vibration. Then a second laser is used to search for transitions between this intermediate state and highly vibrationally excited states. When one of these transitions is found, HCN molecules are transferred to a highly excited vibrational state. Third, a ultraviolet laser photodissociates the highly excited molecules to produce H and CN radicals in its A 2Pi electronic state. Finally, a fourth laser (probe) detects the presence of the CN(A) photofragments by means of an A-->B-->X laser induced fluorescence scheme. The spectra obtained with this technique, consisting of several rotationally resolved vibrational bands, have been analyzed. The positions and rotational parameters of the states observed are presented and compared with the results of a state-of-the-art variational calculation.     

Synthesis and infrared characterization of Br-HBr and Br-DBr entrance channel complexes in solid parahydrogen

We report high resolution vibrational spectra in the HBr (2560 cm(-1)) and DBr (1840 cm(-1)) stretching regions for Br-HBr and Br-DBr entrance channel complexes isolated in solid parahydrogen (pH2). The Br-HBr complexes are generated by synthesizing solid pH2 crystals doped with trace amounts of HBr/Br2 mixtures followed by 355 nm in situ photodissociation of Br2 to form Br atoms. After photolysis is complete, the solid is warmed from 2 to 4.3 K resulting in the irreversible formation of Br-HBr complexes. The large 36.63 cm(-1) HBr monomer-to-complex induced vibrational shift to lower energy measured in these studies is consistent with the linear Br-HBr hydrogen bonded structure predicted from theory. The 0.02 cm(-1) Br-HBr absorption linewidths indicate a 1 ns vibrational excited state lifetime for these entrance channel complexes in solid pH2.