Infrared studies of lead(II) halide-1,10-phenanthroline photosensitive materials

Infrared spectroscopic studies of 1:1 and 1:2 complexes of lead(II) bromide and lead(II) iodide with 1,10-phenanthroline were reported. Vibrational assignments are made by comparison to reported spectra of the uncomplexed 1,10-phenanthroline molecule. Small shifts of the ligand vibrational bands are characteristic of the complexes.     

Vibrational analysis of free and hydrogen bonded complexes of nicotinamide and picolinamide

Harmonic and anharmonic vibrations of free nicotinamide (NIA) and picolinamide (PIA) molecules together with their hydrogen bonded complexes H₂O–NIA and H₂O–PIA have been studied by means of density functional method. The calculation results of the vibrational spectra of free molecules have been investigated and are compared to the available experimental spectra. The vibrational wavenumbers of both molecules have also been calculated by polarizable continuum model (PCM) that represents the solvent as a polarizable continuum and places the solute in a cavity within the solvent (water is chosen as the solvent in this study). The results of PCM calculations and the H₂O–NIA, H₂O–PIA complexes, are used to investigate the H-bonding interactions of both molecules with the water molecule. The harmonic wavenumbers have been scaled by proper factors obtained by comparing the observed versus calculated wavenumbers and it is shown that anharmonic corrections on the vibrational spectra provided a better agreement between the observed and calculated wavenumbers compared to the results obtained by scaling factor method.     

The structures of vanadium oxide cluster-ethene complexes. A combined IR multiple photon dissociation spectroscopy and DFT calculation study

Infrared spectra of complexes of small vanadium oxide clusters with ethene are determined using infrared multiple photon dissociation (IR-MPD) spectroscopy in the range of 550-1850 cm-1. The structures of the complexes have been identified by comparison of the experimental spectra with the harmonic vibrational frequencies and corresponding IR intensities of possible isomers calculated with DFT methods. We find that the ethene molecule binds directly to a vanadium atom in the cluster, although this it is not in all cases the most stable arrangement.     

Solid-liquid-liquid extraction as an approach to the sensitive detection of a hydrophobic pollutant through surface-enhanced Raman spectroscopy

Surface-enhanced Raman scattering (SERS) spectra of thiram (tetramethylthiuram disulfide), a dimethyl dithiocarbamate fungicide, were recorded after the adsorption on plasmonic silver nanowires from a system of water, organic solvent and nanoparticles. As organic solvents dichloromethane and 1-octanol were involved. A method for measuring the adsorption constant of thiram as a model molecule to the silver surface by studying its partition phenomena in a binary solvent system is presented. The method is based on the extraction of a hydrophobic molecule from an organic solvent by an aqueous suspension of silver anisotropic nanoparticles. The obtained results demonstrate the effectiveness of SERS methodology for the sensitive analysis of compounds with low aqueous solubility, and a reliable SERS spectrum of thiram was obtained with excellent signal/noise ratio at low concentrations. In addition, for vibrational assignments, Density Functional Theory (DFT) was used for the simulation of the Raman and SERS spectra of thiram and its complexes with silver considering the following two models: a single silver atom and an Ag₂₀ cluster.     

Understanding Solvent Effects in Vibrational Circular Dichroism Spectra: [1,1'-Binaphthalene]-2,2'-diol in Dichloromethane, Acetonitrile, and Dimethyl Sulfoxide Solvents

We present a combined experimental and computational investigation of the vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of [1,1'-binaphthalene]-2,2'-diol. First, the sensitive dependence of the experimental VA and VCD spectra on the solvent is demonstrated by comparing the experimental spectra measured in CH(2)Cl(2), CD(3)CN, and DMSO-d(6) solvents. Then, by comparing calculations performed for the isolated solute molecule to calculations performed for molecular complexes formed between solute and solvent molecules, we identify three main types of perturbations that affect the shape of the VA and VCD spectra when going from one solvent to another. These sources of perturbations are (1) perturbation of the Boltzmann populations, (2) perturbation of the electronic structure, and (3) perturbation of the normal modes.     

Vibrational analysis of I2*- x nCO2 clusters (n = 1-10): a first principle study on microsolvation

Structure, stability, and vibrational IR and Raman spectra of I(2)(*-) x nCO(2) clusters (n = 1-10) are reported based on first-principle electronic structure calculations. Several close-lying minimum energy structures are predicted for these solvated clusters following the quasi Newton-Raphson procedure of geometry optimization. Search strategy based on Monte-Carlo simulated annealing is also applied to find out the global minimum energy structures of these clusters. Successive addition of solvent CO(2) molecules to the negatively charged diatomic solute, I(2)(*-), is fairly symmetrical. Energy parameters of these solvated clusters are calculated following second-order Moller-Plesset perturbation (MP2) as well as coupled cluster theory with 6-311+G(d) set of basis function (I atom is treated with 6-311G(d) set of basis function). The excess electron in these solvated clusters is observed to be localized mainly over the two I atoms. Average interaction energy between the anionic solute, I(2)(*-), and a solvent CO(2) molecule is approximately 129 meV in I(2)(*-) x nCO(2) clusters, and the average interaction energy between two solvent CO(2) molecules is approximately 85 meV in the case of neutral (CO(2))(n) clusters at MP2 level of theory. IR spectra show similar features in all these solvated clusters, depicting a strong band at approximately 2330 cm(-1) for C-O stretching and a weak band at approximately 650 cm(-1) for CO(2) bending modes. Degeneracy of the bending mode of a free solvent CO(2) unit gets lifted when it interacts with the charged solute I(2)(*-) to form a molecular cluster because of the change in structure of solvent CO(2) units. The vibrational band at the bending region of CO(2) in the Raman spectra of these anionic clusters shows a characteristic feature for the formation of I(2)(*-) x nCO(2) clusters showing a Raman band at approximately 650 cm(-1).     

Simulations of the temperature dependence of amide I vibration

For spectroscopic studies of peptide and protein thermal denaturation it is important to single out the contribution of the solvent to the spectral changes from those originated in the molecular structure. To obtain insights into the origin and size of the temperature solvent effects on the amide I spectra, combined molecular dynamics and density functional simulations were performed with the model N-methylacetamide molecule (NMA). The computations well reproduced frequency and intensity changes previously observed in aqueous NMA solutions. An empirical correction of vacuum frequencies in single NMA molecule based on the electrostatic potential of the water molecules provided superior results to a direct density functional average obtained for a limited number of solute-solvent clusters. The results thus confirm that the all-atom quantum and molecular mechanics approach captures the overall influence of the temperature dependent solvent properties on the amide I spectra and can improve the accuracy and reliability of molecular structural studies.     

High-resolution infrared spectroscopy of HCN-Agn (n = 1-4) complexes solvated in superfluid helium droplets

High-resolution infrared spectroscopy has been used to determine the structures, C-H stretching frequencies, and dipole moments of the HCN-Agn (n = 1-3) complexes formed in superfluid helium droplets. The HCN-Ag4 cluster was tentatively assigned based upon pick-up cell pressure dependencies and harmonic vibrational shift calculations. Ab initio and density functional theory calculations were used in conjunction with the high-resolution spectra to analyze the bonding nature of each cluster. All monoligated species reported here are bound through the nitrogen end of the HCN molecule. The HCN-Agn complexes are structurally similar to the previously reported HCN-Cun clusters, with the exception of the HCN-Ag binary complex. Although the interaction between the HCN and the Agn clusters follows the same trends as the HCN-Cun clusters, the more diffuse nature of the electrons surrounding the silver atoms results in a much weaker interaction.     

SOLUTE-SOLVENT INTERACTION AND ITS EFFECT ON THE VIBRONIC AND VIBRATIONAL STRUCTURE OF PYRENE SPECTRA

Abstract— The enhancement of weakly allowed electronic and vibrational transitions of pyrene in polar solvents at room temperature has been studied by optical and infrared techniques. We previously reported the formation of molecular complexes between pyrene and alcohols by monitoring the changes in the fundamental stretching vibrational band of the —OH group of alcohols in the presence of pyrene. The infrared spectrum of pyrene in the region 1575–1700cm^-1 has been found in the present work to undergo changes in polar solvents, consistent with complex formation, with the appearance of new bands at wavenumbers where symmetry-forbidden transitions exist. The enhancement of weak bands in the electronic spectra is attributed to the reduction in the symmetry of the pyrene molecule brought about by complex formation. Further support for this interpretation is provided by the finding that I-methylpyrene, which has reduced symmetry, shows the enhancement in the electronic spectra and the appearance of new bands in the infrared spectra even in inert solvents. The anomalous behavior of aromatic solvents is discussed.     

Vibrationally quantum-state-specific dynamics of the reactions of CN radicals with organic molecules in solution

The dynamics of reactions of CN radicals with cyclohexane, d(12)-cyclohexane, and tetramethylsilane have been studied in solutions of chloroform, dichloromethane, and the deuterated variants of these solvents using ultraviolet photolysis of ICN to initiate a reaction. The H(D)-atom abstraction reactions produce HCN (DCN) that is probed in absorption with sub-picosecond time resolution using ～500 cm(-1) bandwidth infrared (IR) pulses in the spectral regions corresponding to C-H (or C-D) and C≡N stretching mode fundamental and hot bands. Equivalent IR spectra were obtained for the reactions of CN radicals with the pure solvents. In all cases, the reaction products are formed at early times with a strong propensity for vibrational excitation of the C-H (or C-D) stretching (v(3)) and H-C-N (D-C-N) bending (v(2)) modes, and for DCN products there is also evidence of vibrational excitation of the v(1) mode, which involves stretching of the C≡N bond. The vibrationally excited products relax to the ground vibrational level of HCN (DCN) with time constants of ～130-270 ps (depending on molecule and solvent), and the majority of the HCN (DCN) in this ground level is formed by vibrational relaxation, instead of directly from the chemical reaction. The time-dependence of reactive production of HCN (DCN) and vibrational relaxation is analysed using a vibrationally quantum-state specific kinetic model. The experimental outcomes are indicative of dynamics of exothermic reactions over an energy surface with an early transition state. Although the presence of the chlorinated solvent may reduce the extent of vibrational excitation of the nascent products, the early-time chemical reaction dynamics in these liquid solvents are deduced to be very similar to those for isolated collisions in the gas phase. The transient IR spectra show additional spectroscopic absorption features centered at 2037 cm(-1) and 2065 cm(-1) (in CHCl(3)) that are assigned, respectively, to CN-solvent complexes and recombination of I atoms with CN radicals to form INC molecules. These products build up rapidly, with respective time constants of 8-26 and 11-22 ps. A further, slower rise in the INC absorption signal (with time constant >500 ps) is attributed to diffusive recombination after escape from the initial solvent cage and accounts for more than 2/3 of the observed INC.     

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n 相似文献   

A combined spectroscopic and theoretical study of dibutyltin diacetate and dilaurate in supercritical CO2

Two organotin catalysts, namely, dibutyltin dilaurate (DBTDL) and dibutyltin diacetate (DBTDA), commonly used in the synthesis of polyurethanes, have been investigated combining vibrational spectroscopic measurements with molecular modeling. The structure and vibrational spectra of the DBTDA molecule have been simulated using density functional theory. Thus, because of the Sn...O interactions, the lowest energy conformer reveals an asymmetrically chelated structure of the acetate groups with a C2v symmetry. The experimental IR spectra of DBTDA and DBTDL diluted in carbon tetrachloride and in supercritical CO2 show unambiguously that these molecules adopt the asymmetrically chelated conformation in the solvent. A new attribution of the main peaks constituting the respective IR spectra of the catalysts could be carried out. Finally, from the IR spectra of the two catalysts diluted in supercritical CO2 reported as a function of time, it was found that both molecules react slightly with CO2. However, their spectrum remains unchanged at the earliest stage of the polymerization, indicating that these molecules preserve a catalytic activity similar to that noted in conventional organic solvent.     

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.     

Vibrational spectral analysis and first hyperpolarizability studies of 1-bromonaphthalene based on ab initio and DFT methods

In this work, the experimental and theoretical vibrational spectra of 1-bromonaphthalene (1-BN) were studied. FTIR and FT Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using ab initio Hartree-Fock and density functional method (B3LYP) with the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FTIR and FT Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The optimized geometric parameters were calculated. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good nonlinear optical (NLO) behaviour. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule.     

Hydrogen bond lifetimes and energetics for solute/solvent complexes studied with 2D-IR vibrational echo spectroscopy

Weak pi hydrogen-bonded solute/solvent complexes are studied with ultrafast two-dimensional infrared (2D-IR) vibrational echo chemical exchange spectroscopy, temperature-dependent IR absorption spectroscopy, and density functional theory calculations. Eight solute/solvent complexes composed of a number of phenol derivatives and various benzene derivatives are investigated. The complexes are formed between the phenol derivative (solute) in a mixed solvent of the benzene derivative and CCl4. The time dependence of the 2D-IR vibrational echo spectra of the phenol hydroxyl stretch is used to directly determine the dissociation and formation rates of the hydrogen-bonded complexes. The dissociation rates of the weak hydrogen bonds are found to be strongly correlated with their formation enthalpies. The correlation can be described with an equation similar to the Arrhenius equation. The results are discussed in terms of transition state theory.     

SPECIFIC SOLVATION OF CHLOROPHYLL a: SOLVENT NUCLEOPHILITY, HYDROGEN BONDING AND STERIC EFFECTS ON ABSORPTION SPECTRA

Abstract— The characteristics of chlorophyll a visible absorption spectra have been analyzed in terms of empirical solvent scales of Lewis basicity (B) and acidity (E) as well as steric constants (E_s) (after Koppel and Palm, 1972; Palm, 1977). The presence or absence of the specific four-band structure in the long-wavelength region depends only on the solvent electron-pair donating capability. In protic solvents the Soret band intensity is suppressed, but, in contrast, the extinction coefficient of its first satellite remains practically constant. This allows us to group spectra into four types according to the Soret-band intensity and the structure of the red-band system and assign them to chlorophyll-solvent complexes formed via 1 or 2 donor-acceptor bonds to central Mg and with and without hydrogen bond(s) to some nucleophilic center of the solute molecule.     

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.     

Infrared spectroscopy of water cluster anions, (H2O)n=3-24-)in the HOH bending region: persistence of the double H-bond acceptor (AA) water molecule in the excess electron binding site of the class I isomers

We report vibrational predissociation spectra of water cluster anions, (H(2)O)(n=)()(3)(-)(24)(-) in the HOH bending region to explore whether the characteristic red-shifted feature associated with electron binding onto a double H-bond acceptor (AA) water molecule survives into the intermediate cluster size regime. The spectra of the "tagged" (H(2)O)(n)()(-).Ar clusters indeed exhibit the signature AA band, but assignment of this motif to a particular isomer is complicated by the fact that argon attachment produces significant population of three isomeric forms (as evidenced by their photoelectron spectra). We therefore also investigated the bare clusters since they can be prepared exclusively in the high binding (isomer class I) form. Because the energy required to dissociate a water molecule from the bare complexes is much larger than the transition energies in the bending region, the resulting (linear) action spectroscopy selectively explores the properties of clusters with most internal energy content. The (H(2)O)(15)(-) predissociation spectrum obtained under these conditions displays a more intense AA feature than was found in the spectra of the Ar tagged species. This observation implies that not only is the AA motif present in the class I isomer, but also that it persists when the clusters contain considerable internal energy.     

Isomer selective infrared spectroscopy of neutral metal clusters

We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80-400 cm(-1) region. The observed spectra for Nb(9)Ar(n) (n=1-4) are different for different values of n. This is explained by the presence of two isomers of Nb(9) that have different affinities towards Ar and the isomer specific infrared spectra are obtained. The structures of the isomers are determined by comparing the observed spectra with the outcome of density-functional theory calculations.     

Theoretical and experimental vibrational study of phenylurea: structure, solvent effect and inclusion process with the beta-cyclodextrin in the solid state

FTIR and Raman vibrational spectroscopic techniques as well as DFT quantum chemical calculation were used for characterizing conformational changes of phenylurea (a herbicide parent molecule) occurring from solid state to aqueous medium. Experimental infrared frequencies were assigned on the base of urea and benzenic derivatives spectroscopic data available in the literature and vibrational normal modes analytical calculation at the fully optimized geometry. Investigation of isotopic and solvent effects has revealed that the structure of phenylurea is particularly sensitive to the electrostatic environment via hydrogen non covalent bonds. The ability of beta-cyclodextrin (beta-CD) to form host-guest inclusion complex with phenylurea in the solid state was also evidenced by significant frequency shifts observed in the 1400-1800 cm(-1) spectral range.