Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(4) in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO(6) octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Infrared-spectroscopic and density-functional-theory investigations of the LaCO, La2[eta2(mu2-C,O)], and c-La2(mu-C)(mu-O) molecules in solid argon

Reactions of laser-ablated lanthanum atoms with CO molecules in solid argon have been studied. The neutral lanthanum monocarbonyl (LaCO), produced upon sample deposition at 7 K, exhibits a C-O stretching frequency of 1772.7 cm(-1); to the best of our knowledge this is the lowest yet observed for a terminal CO in a neutral metal-carbonyl molecule (MCO, M = metal atom), implying anomalously enhanced metal-to-CO back-bonding. The infrared (IR) absorption band at 1145.9 cm(-1) is assigned to the C-O stretching mode of the side-on-bonding CO in the La2[eta2(mu2-C,O)] molecule. This CO-activated molecule undergoes an UV/Vis-photoinduced rearrangement to the CO-dissociated molecule, c-La2(mu-C)(mu-O). Density functional theory (DFT) calculations have been performed on these molecules, the results of which lend strong support to the experimental assignments of the IR spectra. LaCO is predicted to have a quartet ground state, corresponding to a linear geometry. Its formation involves La 6s-->4f promotion, which increases the strength of La-CO bonding by decreasing the sigma repulsion and, remarkably, by increasing the La 5d and 4f-->CO 2pi back-bonding. The observations schematically depict the whole process, starting with the interaction of CO with metal and ending with CO dissociation by the lanthanum dimer.     

Ion core structure in (C(2)n+ and (CS2)n- (n=3-10) studied by infrared photodissociation spectroscopy

Infrared photodissociation spectra of (CS(2))(n) (+) and (CS(2))(n) (-) with n=3-10 are measured in the 1100-2000 cm(-1) region. All the (CS(2))(n) (+) clusters exhibit three bands at approximately 1410, approximately 1490, and approximately 1540 cm(-1). The intensity of the 1540 cm(-1) band relative to those of the other bands increases with increasing the cluster size, indicating that the band at 1540 cm(-1) is assignable to the antisymmetric CS stretching vibration of solvent CS(2) molecules in the clusters. On the basis of density functional theory calculations, the 1410 and 1490 cm(-1) bands of (CS(2))(n) (+) are assigned to CS stretching vibrations of the C(2)S(4) (+) cation core with a C(2) form. The (CS(2))(n) (-) clusters show two bands at around 1215 and 1530 cm(-1). Similar to the case of cation clusters, the latter band is ascribed to the antisymmetric CS stretching vibration of solvent CS(2) molecules. Vibrational frequency analysis of CS(2) (-) and C(2)S(4) (-) suggests that the 1215 cm(-1) band is attributed to the antisymmetric CS stretching vibration of the CS(2) (-) anion core with a C(2v) structure.     

Infrared absorption of CH3OSO detected with time-resolved Fourier-transform spectroscopy

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to detect temporally resolved infrared absorption spectra of CH(3)OSO produced upon irradiation of a flowing gaseous mixture of CH(3)OS(O)Cl in N(2) or CO(2) at 248 nm. Two intense transient features with origins near 1152 and 994 cm(-1) are assigned to syn-CH(3)OSO; the former is attributed to overlapping bands at 1154 ± 3 and 1151 ± 3 cm(-1), assigned to the S=O stretching mixed with CH(3) rocking (ν(8)) and the S=O stretching mixed with CH(3) wagging (ν(9)) modes, respectively, and the latter to the C-O stretching (ν(10)) mode at 994 ± 6 cm(-1). Two weak bands at 2991 ± 6 and 2956 ± 3 cm(-1) are assigned as the CH(3) antisymmetric stretching (ν(2)) and symmetric stretching (ν(3)) modes, respectively. Observed vibrational transition wavenumbers agree satisfactorily with those predicted with quantum-chemical calculations at level B3P86∕aug-cc-pVTZ. Based on rotational parameters predicted at that level, the simulated rotational contours of these bands agree satisfactorily with experimental results. The simulation indicates that the S=O stretching mode of anti-CH(3)OSO near 1164 cm(-1) likely makes a small contribution to the observed band near 1152 cm(-1). A simple kinetic model of self-reaction is employed to account for the decay of CH(3)OSO and yields a second-order rate coefficient k=(4 ± 2)×10(-10) cm(3)molecule(-1)s(-1).     

Infrared spectra of the M(NO)n (M = Sn, Pb; n = 1, 2) and PbNO- molecules

Reactions of laser-ablated tin and lead atoms with nitric oxide molecules in solid argon and neon have been investigated using matrix-isolation infrared spectroscopy. In the argon experiments, absorptions at 1560.1, 1625.8, and 1486.7 cm(-1) are assigned to the N-O stretching vibrations of the SnNO and Sn(NO)2 molecules, and absorptions at 1541.9, 1630.0, 1481.8, and 1457.5 cm(-1) are assigned to the N-O stretching vibrations of the PbNO, Pb(NO)2, and PbNO- molecules on the basis of isotopic shifts and splitting patterns. The present neon experiments only produce neutral tin and lead mononitrosyls. Density functional theory calculations have been performed on these tin and lead nitrosyls. The good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts substantiates the identification of these nitrosyls from the matrix infrared spectra.     

Measurement and revised analysis of the torsional combination band of the nonpolar N2O dimer at 2249 cm(-1)

The high-resolution infrared spectrum of the weakly-bound dimer (N(2)O)(2) is studied using a rapid-scan tunable-diode laser spectrometer to probe a pulsed supersonic jet expansion. An observed band with c-type rotational structure is assigned as a combination of the intramolecular N(2)O nu(1) stretching vibration and the intermolecular out-of-plane dimer torsional vibration, with a vibrational origin at 2249.360 cm(-1). The resulting torsional frequency for the nonpolar N(2)O dimer is about 21.5 cm(-1). The present rotational analysis is completely different from that reported previously for the same band [Hecker et al., Phys. Chem. Chem. Phys., 2003, 5, 2333], which gave a band origin some 1.53 cm(-1) lower.     

Infra-red and Raman spectroscopic study of tetra-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with tert-butyl derivatives

The infra-red spectroscopic data for a series of 13 homoleptic substituted bis(phthalocyaninato) rare earth complexes with tervalent rare earths M(III)(TBPc)(2) [M=Y, Pr, ..., Lu except La, Ce and Pm; TBPc=dianion of 3(4),12(13),21(22),30(31)-tetra(tert-butyl)-phthalocyanine] have been collected with resolution of 2 cm(-1). Raman spectroscopic properties in the range of 500-1,800 cm(-1) for these double-deckers M(III)(TBPc)(2) have been collected using laser excitation sources emitting at 632.8 nm. Both the IR and Raman spectra for M(III)(TBPc)(2) are more complicated than those of homoleptic bis(phthalocyaninato) rare earth analogues due to the decreased molecular symmetry of these double-decker compounds. For this series, the IR typical marker band of (TBPc)(-) appears as an intense absorption at 1,314-1,319 cm(-1), attributed to the pyrrole stretching. Under excitation at 632.8 nm that is in close resonance with the main Q absorption band of phthalocyanine ligand, typical Raman marker band of the monoanion radical (TBPc)(-) was observed at 1,515-1,530 cm(-1) resulting from aza CN stretching. Both techniques reveal that the frequencies of pyrrole stretching, isoindole breathing and aza stretchings depend on the rare earth ionic size, shifting to higher energy along with the lanthanide contraction due to the increased ring-ring interaction across the series.     

Infrared spectra and quantum chemical calculations of the uranium-carbon molecules UC, CUC, UCH, and U(CC)2

Laser evaporation of carbon rich uranium/carbon alloy targets into condensing argon or neon matrix samples gives weak infrared absorptions that increase on annealing, which can be assigned to new uranium carbon bearing species. New bands at 827.6 cm(-1) in solid argon or 871.7 cm(-1) in neon become doublets with mixed carbon 12 and 13 isotopes and exhibit the 1.0381 carbon isotopic frequency ratio for the UC diatomic molecule. Another new band at 891.4 cm(-1) in argon gives a three-band mixed isotopic spectrum with the 1.0366 carbon isotopic frequency ratio, which is characteristic of the anti-symmetric stretching vibration of a linear CUC molecule. No evidence was found for the lower energy cyclic U(CC) isomer. Other bands at 798.6 and 544.0 cm(-1) are identified as UCH, which has a uranium-carbon triple bond similar to that in UC. Evidence is found for bicyclic U(CC)(2) and tricyclic U(CC)(3). This work shows that U and C atoms react spontaneously to form the uranium carbide U≡C and C≡U≡C molecules with uranium-carbon triple bonds.     

Infrared spectroscopic characteristics of octa-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with (4-methoxy)phenoxy derivatives

The infrared (IR) spectroscopic data for a series of 15 rare earth double-deckers M[Pc(MeOPhO)(8)](2) [M=Y, La, ..., Lu, except Pm; H(2)Pc=2, 3, 9, 10, 16, 17, 23, 24-octakis(4-methoxyphenoxy)phthalocyanine] with tervalent rare earths M(III)[Pc(MeOPhO)(8)](2) (M=Y, La, ..., Lu except Ce and Pm) and intermediate-valent cerium Ce[Pc(MeOPhO)(8)](2) have been collected with resolution of 2cm(-1). For M(III)[Pc(MeOPhO)(8)](2), typical IR marker band of the monoradical anion Pc(MeOPhO)(8)(-) shows characteristic absorption band whose frequency linearly varies in the range from 1,313 cm(-1) as a weak band for La[Pc(MeOPhO)(8)](2) to 1,324 cm(-1) as a medium band for Lu[Pc(MeOPhO)(8)](2) along with the decrease of rare earth ionic size. For Ce[Pc(MeOPhO)(8)](2), a weak band at 1,324 cm(-1) with contribution from pyrrole stretching was the marker IR band of phthalocyanine dianion Pc(2-). In conclusion, all the metal size-dependent IR absorptions should be contributed primarily from the vibrations of pyrrole, isoindole stretching, breathing or deformation or aza stretching of the Pc ring.     

Revealing anharmonic couplings and energy relaxation in DNA oligomers by ultrafast infrared spectroscopy

The identification and characterization of NH 2 hydrogen-bonded stretching vibrations [nu(NH 2)] in DNA oligomers is usually hampered by the all-dominating absorption of the water stretching band in the spectral range of 3050-3600 cm(-1). Here, we use the two-color IR pump-probe technique to overcome the limitations of linear absorption spectroscopy by exciting adenine-thymine (A-T) oligomer vibrations in the fingerprint region and analyzing induced transient spectral changes in the nu(NH2) spectral region. These transient changes are related to anharmonic couplings to the modes excited in the fingerprint region and to modes populated by intra- and intermolecular energy redistribution and relaxation. The combination of calculated anharmonic coupling parameters and experimental transient IR data allows the assignment of a transition at 3215 cm(-1) to the nu(NH2) vibration of adenine in dA(20)-dT(20) DNA oligomers.     

Infrared spectra of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes. Part 3. The effects of substituents and molecular symmetry on the infrared characteristics of phthalocyanine in bis(phthalocyaninato) rare earth complexes

The infra-red (IR) spectroscopic data for a series of 45 homoleptic unsubstituted and substituted bis(phthalocyaninato) rare earth complexes M(Pc)2 and M(Pc*)2 [M=Y, La...Lu except Pm; H2Pc=phthalocyanine; H2Pc*=2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyanine (H2OOPc) and 2(3),9(10),16(17),24(25)-tetra(tert-butyl)phthalocyanine (H2TBPc)] have been collected with resolution of 2 cm(-1). The IR spectra for M(Pc)2 and M(OOPc)2 are much simpler than those of M(TBPc)2, revealing the relatively higher symmetry of the former two compounds. For M(Pc)2 the Pc-* marker band at 1312-1323 cm(-1), attributed to the pyrrole stretching, and the isoindole stretching band at 1439-1454 cm(-1) are found to be dependent on the central rare earth size, shifting slightly to the higher energy along with the decrease of rare earth radius. The frequency of the vibration at 876-887 cm(-1) is also dependent on the rare earth ionic size. The metal size-sensitivity of this band and theoretical studies render it possible to re-assign it to the coupling of isoindole deformation and aza vibration. The nature of another metal-sensitive vibration mode at 1110-1116 cm(-1), which was previously assigned to the C-H bending, is now re-assigned as an isoindole breathing mode with some small contribution also from C-H in-plane bending. These assignments are supported by comparative studies of the IR spectra of substituted bis(phthalocyaninato) analogues M(OOPc)2 and M(TBPc)2. By comparison between the IR spectra of unsubstituted and substituted bis(phthalocyaninato) rare earth analogues and according to the IR characteristics of alkyl groups, some characteristic vibrational fundamentals due to the Pc rings and the substituents can be separately identified. In conclusion, all the metal size-dependent IR absorptions are composed primarily of the vibrations of pyrrole or isoindole stretching, breathing or deformation or aza stretching of the Pc ring.     

Spectroscopic characterization of chromite from the Moa-Baracoa Ophiolitic Massif, Cuba

The Cuban chromites with a spinel structure, FeCr2O4 have been studied using optical absorption and EPR spectroscopy. The spectral features in the electronic spectra are used to map the octahedral and tetrahedral co-ordinated cations. Bands due Cr3+ and Fe3+ ions could be distinguished from UV-vis spectrum. Chromite spectrum shows two spin allowed bands at 17,390 and 23,810 cm(-1) due to Cr3+ in octahedral field and they are assigned to 4A2g(F) --> 4T2g(F) and 4A2g(F) --> 4T1g(F) transitions. This is in conformity with the broad resonance of Cr3+ observed from EPR spectrum at g = 1.903 and a weak signal at g = 3.861 confirms Fe3+ impurity in the mineral. Bands of Fe3+ ion in the optical spectrum at 13,700, 18,870 and 28,570 cm(-1) are attributed to 6A1g(S) --> 4T1g(G), 6A1g(S) --> 4T2g(G) and 6A1g(S) --> 4T2g(P) transitions, respectively. Near-IR reflectance spectroscopy has been used effectively to show intense absorption bands caused by electronic spin allowed d-d transitions of Fe2+ in tetrahedral symmetry, in the region 5000-4000 cm(-1). The high frequency region (7500-6500 cm(-1)) is attributed to the overtones of hydroxyl stretching modes. Correlation between Raman spectral features and mineral chemistry are used to interpret the Raman data. The Raman spectrum of chromite shows three bands in the CrO stretching region at 730, 560 and 445 cm(-1). The most intense peak at 730 cm(-1) is identified as symmetric stretching vibrational mode, A1g(nu1) and the other two minor peaks at 560 and 445 cm(-1) are assigned to F2g(nu4) and E(g)(nu2) modes, respectively. Cation substitution in chromite results various changes both in Raman and IR spectra. In the low-wavenumber region of Raman spectrum a significant band at 250 cm(-1) with a component at 218 cm(-1) is attributed F2g(nu3) mode. The minor peaks at 195, 175, 160 cm(-1) might be due to E(g) and F2g symmetries. Broadening of the peak of A1g mode and shifting of the peak to higher wavenumber observed as a result of increasing the proportion of Al3+O6. The presence of water in the mineral shows bands in the IR spectrum at 3550, 3425, 3295, 1630 and 1455 cm(-1). The vibrational spectrum of chromite gives raise to four frequencies at 985, 770, 710 and 650 cm(-1). The first two frequencies nu1 and nu2 are related to the lattice vibrations of octahedral groups. Due to the influence of tetrahedral bivalent cation, vibrational interactions occur between nu3 and nu4 and hence the low frequency bands, nu3 and nu4 correspond to complex vibrations involving both octahedral and tetrahedral cations simultaneously. Cr3+ in Cuban natural chromites has highest CFSE (20,868 cm(-1)) when compared to other oxide minerals.     

Infrared measurements and calculations on H2O.HO

We have measured the infrared spectrum of H2O.HO in argon matrices at 11.5 +/- 0.5 K. We have also calculated the vibrational frequencies and intensities of the H2O.HO complex. As a result of these measurements and calculations, we have assigned a previously unassigned absorption band at 3442.1 cm-1 to the OH stretch in the radical complexed to the water molecule. This absorption originates from a complex that is situated in a different site within the argon matrix to those absorptions already assigned to this vibration at 3452.2 and 3428.0 cm-1. We observe a decrease in intensity of the OH radical stretching vibration of the H2O.HO complex upon isotopic substitution of D for H that agrees well with our calculations.     

The characterisation of molecular alkali-metal azides

Matrix isolation infrared (IR) studies have been carried out on the vaporisation of the alkali-metal azides MN3 (M = Na, K, Rb and Cs). The results show that under high vacuum conditions, molecular KN3, RbN3 and CsN3 are present as stable high-temperature vapour species, together with variable amounts of nitrogen gas and the corresponding metal atoms. The characterisation of these molecular azides is supported by ab initio molecular orbital calculations and density functional theory (DFT) calculations, and for CsN3 in particular, by the detection of the isotopomers Cs(14N15N14N) and Cs(15N14N14N). The IR spectra are assigned to a "side-on" (C(2v)) structure by comparison with the spectral features predicted both by vibrational analysis and calculation. The most intense IR features for KN3, RbN3 and CsN3 isolated in nitrogen matrices lie at 2005, 2004.4 and 2002.2 cm(-1), respectively, and correspond to the N3 asymmetric stretch. The N3 bending mode in CsN3 is identified at 629 cm(-1). An additional feature routinely observed in these experiments occurred at approximately 2323 cm(-1) and is assigned to molecular N2, perturbed by the close proximity of an alkali-metal atom. The position of this band appeared to show very little cation dependence, but its intensity correlated with the extent of sample thermal decomposition.     

Raman under nitrogen. The high-resolution Raman spectroscopy of crystalline uranocene, thorocene, and ferrocene

The utility of recording Raman spectroscopy under liquid nitrogen, a technique we call Raman under nitrogen (RUN), is demonstrated for ferrocene, uranocene, and thorocene. Using RUN, low-temperature (liquid nitrogen cooled) Raman spectra for these compounds exhibit higher resolution than previous studies, and new vibrational features are reported. The first Raman spectra of crystalline uranocene at 77 K are reported using excitation from argon (5145 A) and krypton (6764 A) ion lasers. The spectra obtained showed bands corresponding to vibrational transitions at 212, 236, 259, 379, 753, 897, 1500, and 3042 cm(-1), assigned to ring-metal-ring stretching, ring-metal tilting, out-of-plane CCC bending, in-plane CCC bending, ring-breathing, C-H bending, CC stretching and CH stretching, respectively. The assigned vibrational bands are compared to those of uranocene in THF, (COT)2-, and thorocene. All vibrational frequencies of the ligands, except the 259 cm(-1) out-of-plane CCC bending mode, were found to increase upon coordination. A broad, polarizable band centered about approximately 460 cm(-1) was also observed. The 460 cm(-1) band is greatly enhanced relative to the vibrational Raman transitions with excitations from the krypton ion laser, which is indicative of an electronic resonance Raman process as has been shown previously. The electronic resonance Raman band is observed to split into three distinct bands at 450, 461, and 474 cm(-1) with 6764 A excitation. Relativistic density functional theory is used to provide theoretical interpretations of the measured spectra.     

Molecular dynamics simulation of liquid methanol. II. Unified assignment of infrared, Raman, and sum frequency generation vibrational spectra in methyl C-H stretching region

Vibrational spectra of methyl C-H stretching region are notoriously complicated, and thus a theoretical method of systematic assignment is strongly called for in condensed phase. Here we develop a unified analysis method of the vibrational spectra, such as infrared (IR), polarized and depolarized Raman, and ssp polarized sum frequency generation (SFG), by flexible and polarizable molecular dynamics simulation. The molecular model for methanol has been developed by charge response kernel model to allow for analyzing the methyl C-H stretching vibrations. The complicated spectral structure by the Fermi resonance has been unraveled by empirically shifting potential parameters, which provides clear information on the coupling mechanism. The analysis confirmed that for the IR, polarized Raman, and SFG spectra, two-band structure at about 2830 and 2950 cm(-1) results from the Fermi resonance splitting of the methyl C-H symmetric stretching and bending overtones. In the IR spectrum, the latter, higher-frequency band is overlapped with prominent asymmetric C-H stretching bands. In the depolarized Raman spectrum, the high frequency band at about 2980 cm(-1) is assigned to the asymmetric C-H stretching mode. In the SFG spectrum, the two bands of the splitted symmetric C-H stretching mode have negative amplitudes of imaginary nonlinear susceptibility χ(2), while the higher-frequency band is partly cancelled by positive imaginary components of asymmetric C-H stretching modes.     

Infrared and infrared emission spectroscopy of nesquehonite Mg(OH)(HCO3)·2H2O-implications for the formula of nesquehonite

The mineral nesquehonite Mg(OH)(HCO(3))·2H(2)O has been analysed by a combination of infrared (IR) and infrared emission spectroscopy (IES). Both techniques show OH vibrations, both stretching and deformation modes. IES proves the OH units are stable up to 450°C. The strong IR band at 934 cm(-1) is evidence for MgOH deformation modes supporting the concept of HCO(3)(-) units in the molecular structure. Infrared bands at 1027, 1052 and 1098 cm(-1) are attributed to the symmetric stretching modes of HCO(3)(-) and CO(3)(2-) units. Infrared bands at 1419, 1439, 1511, and 1528 cm(-1) are assigned to the antisymmetric stretching modes of CO(3)(2-) and HCO(3)(-) units. IES supported by thermoanalytical results defines the thermal stability of nesquehonite. IES defines the changes in the molecular structure of nesquehonite with temperature. The results of IR and IES supports the concept that the formula of nesquehonite is better defined as Mg(OH)(HCO(3))·2H(2)O.     

Vibrational spectra of 1-methyluracilate complex with silver(I) and theoretical studies of the 1-MeU anion

The FT-Raman and FT-infrared spectra of (1-methyluracilato)silver, [Ag(C(5)H(5)N(2)O(2))] in the solid state have been studied. The complex is a polymer in which one silver ion is linearly bonded to two 1-MeU ligands through the deprotonated N(3) sites and another silver ion is tetrahedrally coordinated to the four 1-MeU ligands through the O2 and O4 carbonyl oxygen atoms. The harmonic vibrational frequencies, infrared intensities and Raman scattering activities of the N(3)-deprotonated 1-methyluracilate anion have been calculated using density functional (B3LYP) and ab initio (HF and MP2) methods with the 6-31G(d,p) and 6-31++G(df,pd) basis sets. The calculated potential energy distribution (PED) for the 1-MeU anion has proved to be of great help in assigning the spectra of the title complex. It can be concluded that the two strong Raman bands at 1263 and 796 cm(-1) are diagnostic for the N3-deprotonation of the 1-methyluracilate ring and complexation with silver ion. The linear N-Ag-N stretching vibrations are assigned to the bands at 448 and 362 cm(-1) (IR) and 453, 362 cm(-1) (Raman). The Ag-O stretching vibrations are assigned to the bands in the range of 280-250 cm(-1).     

CO adsorption on CoMo and NiMo sulfide catalysts: a combined IR and DFT study

Experimental IR spectra of carbon monoxide adsorbed on a series of Mo/Al2O3, CoMo/Al2O3, and NiMo/Al2O3 sulfided catalysts have been compared to ab initio DFT calculations of CO adsorption on CoMo and NiMo model surfaces. This approach allows the main IR features of CO adsorbed on the sulfide phase to be assigned with an uncertainty of 15 cm(-1). On the CoMo system, the band at 2070 cm(-1) is specific of the promotion by Co and is assigned to CO interacting either with a Co atom or with a Mo atom adjacent to a Co atom. On the NiMo system, CO adsorption on Ni centers of the promoted phase leads to a high-wavenumber band at approximately 2120 cm(-1) that strongly overlaps the band at 2110 cm(-1) characteristic of nonpromoted Mo sites. For NiMo and CoMo catalysts, broad shoulders at low wave numbers (below 2060 cm(-1)) are characteristic of Mo centers adjacent to promoter atoms, indicating a partial decoration of the MoS2 edges by the promoter.     

Raman spectroscopic study on solvation of diphenylcyclopropenone and phenol blue in room temperature ionic liquids

We investigated the solvation of several room temperature ionic liquids by Raman spectroscopy using diphenylcyclopropenone (DPCP) and phenol blue (PB) as probe molecules. We estimated acceptor numbers (AN) of room temperature ionic liquids by an empirical equation associated with the Raman band of DPCP assigned as a C=C stretching mode involving a significant C=O stretching character. According to the dependence of AN on cation and anion species, the Lewis acidity of ionic liquids is considered to come mainly from the cation charge. The frequencies and bandwidths of the C=O and C=N stretching modes of phenol blue are found to be close to those in conventional polar solvents such as methanol and dimethyl sulfoxide. The frequencies of these vibrational modes show similar dependence upon the electronic absorption band center as is observed in conventional liquid solvents. However, peculiar behavior was found in the Raman bandwidths and the excitation wavelength dependence of the C=N stretching mode in room temperature ionic liquids. Both the bandwidth of the C=N stretching mode and the extent of the excitation wavelength dependence of the Raman shift of the C=N stretching mode tend to decrease as the absorption band center decreases, in contrast to the case of conventional solvents. This anomaly is discussed in terms of the properties of room temperature ionic liquids.