Infrared absorption of C6H5SO2 detected with time-resolved Fourier-transform spectroscopy

C6H5SO2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm-1 are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br/SO2/CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396 cm-1 ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed.     

Theoretical Raman and infrared spectra, and vibrational assignment for para-halogenoanilines: DFT study

The theoretical IR and Raman spectra of para-halogenoanilines, 4-XC(6)H(4)NH(2) (X=F, Cl and Br) were calculated by using the density functional B3LYP method with the 6-311++G(df,pd) basis set. The theoretical spectra show very good agreement with experiment. The rigorous normal coordinate analyses have been performed, and the detailed vibrational assignment has been made on the basis of the calculated potential energy distributions (PEDs). Several ambiguities and contradictions in the previously reported vibrational assignments have been clarified. The "marker bands" and the effects of the halogen substituent on the characteristic aniline bands in the IR and Raman spectra are discussed.     

Ab initio and DFT studies on vibrational spectra of some mixed carbonyl-halide complexes of ruthenium(II)

The vibrational spectra of Ru(CO)6(2+) and some of its mixed carbonyl-halide complexes, cis-Ru(CO)2X4(2-), fac-Ru(CO)3X3- and Ru(CO)5X+ (X = F, Cl, Br and I), have been systematically investigated by ab initio RHF and density functional B3LYP methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of complexes Ru(CO)6(2+), cis-Ru(CO)2X4(2-) and fac-Ru(CO)3X3- are evaluated via comparison with the experimental values. In the infrared frequency region, the C-O stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations less than 5%. In the far-infrared region, the B3LYP/SDD method achieved the best results with deviations less than 8% for Ru-X stretching and less than 2% for Ru-C stretching vibrational frequencies. The vibrational frequencies for Ru(CO)5X+ that have not been experimentally reported were predicted.     

Infrared vacuum-ultraviolet laser pulsed field ionization-photoelectron study of CH3Br+ (X(2)E(3/2))

By preparing methyl bromide (CH3Br) in selected rotational levels of the CH3Br(X(1)A1; v1 = 1) state with infrared (IR) laser excitation prior to vacuum-ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have observed rotationally resolved photoionization transitions to the CH3Br(+)(X(2)E(3/2); v1(+) = 1) state, where v1 and v1(+) are the symmetric C-H stretching vibrational mode for the neutral and cation, respectively. The VUV-PFI-PE origin band for CH3Br(+)(X(2)E(3/2)) has also been measured. The simulation of these IR-VUV-PFI-PE and VUV-PFI-PE spectra have allowed the determination of the v1(+) vibrational frequency (2901.8 +/- 0.5 cm(-1)) and the ionization energies of the origin band (85 028.3 +/- 0.5 cm(-1)) and the v1(+) = 1 <-- v1 = 1 band (84 957.9 +/- 0.5 cm(-1)).     

Theoretical studies on vibrational spectra of some mixed carbonyl-halide complexes of Osmium(II)

The vibrational spectra of Os(CO)(6)(2+) and some of its mixed carbonyl-halide complexes, cis-Os(CO)(2)X(4)(2-), fac-Os(CO)(3)X(3)(-) and Os(CO)(5)X(+) (X=F, Cl, Br and I), have been systematically investigated by ab initio RHF and density functional B3LYP methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of complexes Os(CO)(6)(2+), cis-Os(CO)(2)X(4)(2-) and fac-Os(CO)(3)X(3)(-) are evaluated via comparison with the experimental values. In infrared frequency region, the C-O stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations less than 5%. In the far-infrared region, the B3LYP/SDD method achieved the best results with deviations less than 9% for Os-X stretching and less than 8% for Os-C stretching vibrational frequencies. The vibrational frequencies for Os(CO)(5)X(+) that have not been experimentally reported were predicted.     

Harmonic and anharmonic features of IR and NIR absorption and VCD spectra of chiral 4-X-[2.2]paracyclophanes

The vibrational absorption spectra and vibrational circular dichroism (VCD) spectra of both enantiomers of 4-X-[2.2]paracyclophanes (X = COOCD3, Cl, I) have been recorded for a few regions in the range of 900-12000 cm(-1). The analysis of the VCD spectra for the two IR regions, 900-1600 cm(-1) and 2800-3200 cm(-1), is conducted by comparing with DFT calculations of the corresponding spectra; the latter region reveals common motifs of vibrational modes for the three molecules for aliphatic CH stretching fundamentals, whereas in the mid-IR region, one is able to identify specific signatures arising from the substituent groups X. In the CH stretching region between 2900 and 2800 cm(-1), we identify and interpret a group of three IR VCD bands due to HCH bending overtone transitions in Fermi resonance with CH stretching fundamental transitions. The analysis of the NIR region between approximately 8000 and approximately 9000 cm(-1) for X = COOCD3 reveals important features of the aromatic CH stretching overtones that are of value since the aromatic CH stretching fundamentals are almost silent. The intensifying of such overtones is attributed to electrical anharmonicity terms, which are evaluated here by ab initio methods and compared with literature data.     

Infrared absorption of gaseous benzoyl radical C6H5CO recorded with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C(6)H(5)CO. C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm or in reactions of phenyl radical (C(6)H(5)) with CO; C(6)H(5) was produced on photolysis of C(6)H(5)Br at 248 nm. One intense band at 1838 ± 1 cm(-1), one weak band at 1131 ± 3 cm(-1), and two extremely weak bands at 1438 ± 5 and 1590 ± 10 cm(-1) are assigned to the C═O stretching (ν(6)), the C-C stretching mixed with C-H deformation (ν(15)), the out-of-phase C(1)C(2)C(3)/C(5)C(6)C(1) symmetric stretching (ν(10)), and the in-phase C(1)C(2)C(3)/C(4)C(5)C(6) antisymmetric stretching (ν(7)) modes of C(6)H(5)CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C(6)H(5)CO isolated in solid Ar and with values predicted for C(6)H(5)CO with the B3LYP/aug-cc-pVDZ method. The rotational contours of the two bands near 1838 and 1131 cm(-1) simulated according to rotational parameters predicted with the B3LYP/aug-cc-pVDZ method fit satisfactorily with the experimental results. Additional products BrCO, C(6)H(5)C(O)Br, and C(6)H(5)C(O)C(6)H(5) were identified in the C(6)H(5)Br/CO/N(2) experiments; the kinetics involving C(6)H(5)CO and C(6)H(5)C(O)Br are discussed.     

Vibrational and Structural Dynamics of Mn(CO)5Br and Re(CO)5Br Examined Using Nonlinear Infrared Spectroscopy

Vibrational and structural dynamics of two transition metal carbonyl complexes, Mn(CO)₅Br and Re(CO)₅Br were examined in DMSO, using ultrafast infrared pump-probe spectroscopy, steady-state linear infrared spectroscopy and quantum chemistry computations. Two carbonyl stretching vibrational modes (a low-frequency A₁ mode and two high-frequency degenerate E modes) were used as vibrational probes. Central metal effect on the CO bond order and force constant was responsible for a larger E-A₁ frequency separation and a generally more red-shifted E and A₁ peaks in the Re complex than in the Mn complex. A generally broader spectral width for the A₁ mode than the E mode is believed to be partially due to vibrational lifetime effect. Vibrational mode-dependent diagonal anharmonicity was observed in transient infrared spectra, with a generally smaller anharmonicity found for the E mode in both the Mn and Re complexes.     

Silylene-bridged dinuclear iron complexes [Cp(OC)2Fe]2SiX2 (X = H,F, Cl,Br, I). Synthesis,molecular structure,vibrational spectroscopy,and theoretical studies

The mu2-silylene-bridged iron complexes [Cp(OC)(2)Fe](2)SiX(2) (X = F (2), Br (4), I (5)) have been prepared from the mu2-SiH(2) functional precursor [Cp(OC)(2)Fe](2)SiH(2) (1) by hydrogen/halogen exchange, using HBF(4), CBr(4), and CH(2)I(2), respectively. The fluoro- and bromo-substituted derivatives 2 and 4 are converted upon UV irradiation to the carbonyl- and dihalosilylene-bridged dinuclear complexes [Cp(OC)Fe](2) (mu2-CO)(mu2-SiX(2)) (X = F (6), Br (7)) via CO elimination. All new compounds have been characterized spectroscopically, and, in addition, the molecular structure of 2, 4, and the previously reported chloro derivative [Cp(OC)(2)Fe](2)SiCl(2) (3) has been determined by single-crystal X-ray diffraction methods. For 1-5, the Fourier transform infrared and Raman spectra have been recorded and discussed, together with density functional theory calculations, which support the experimental results of the structural and vibrational analysis. The computed geometries, harmonic vibrational wavenumbers, and their corresponding Raman scattering activities are in good agreement with the experimental data. A significant dependence of the CO and Fe-Si stretching modes on the X substituents of the mu2-silylene bridge has been observed and discussed.     

Low-energy vibrations of the group 10 metal monocarbonyl MCO (M = Ni, Pd, and Pt): rotational spectroscopy and force field analysis

The rotational spectra of NiCO and PdCO in the ground and ν(2) excited vibrational states were observed by employing a source-modulated microwave spectrometer. The NiCO and PdCO molecules were generated in a free space cell by the sputtering reaction of nickel and palladium sheets, respectively, lining the inner surface of a stainless steel cathode with a dc glow plasma of CO and Ar. The molecular constants of NiCO and PdCO were determined by least-squares analysis. By force field analysis for the molecular constants of not only NiCO and PdCO but also of PtCO as previously reported, the harmonic force constants were determined for these three group 10 metal monocarbonyls. The vibrational wavenumbers derived for the lower M-C stretching vibrations were in good agreement with those obtained from the IR spectra in noble gas matrices and those predicted by several quantum chemical calculations published in the past. The bending vibrational wavenumbers derived by the force field analysis were also consistent with most quantum chemical calculations previously reported, but showed systematic discrepancies from the matrix IR values by about 40 cm(-1), even after reassignment (ν(2) band → 2ν(2) band) of the matrix IR spectra of PdCO and PtCO.     

Vibrational frequencies, force constants, mean amplitudes, shrinkage effects and thermodynamic functions for monohaloacetylenes

Harmonic force fields are developed for the monohaloacetylenes on the basis of recent vibrational spectra of H-CC-I and previously published spectra of H-CC-X (X = F, Cl, Br). Mean amplitudes of vibration and Bastiansen-Morino shrinkage effects are reported for monohaloacetylenes and their deuterated derivatives. Thermodynamic functions are listed for monoiodoacetylene.     

Infrared photodissociation spectroscopy of mononuclear iron carbonyl anions

The infrared photodissociation spectroscopy of mass-selected mononuclear iron carbonyl anions Fe(CO)(n)(-) (n = 2-8) were studied in the carbonyl stretching frequency region. The FeCO(-) anion does not fragment when excited with infrared light. Only a single IR active band was observed for the Fe(CO)(2)(-) and Fe(CO)(3)(-) anions, consistent with theoretical predictions that these complexes have linear D(∞h) and planar D(3h) symmetry, respectively. The Fe(CO)(4)(-) anion is the most intense peak in the mass spectra and was characterized to have a completed coordination sphere with high stability. Anion clusters larger than n = 4 were determined to involve a Fe(CO)(4)(-) core anion that is progressively solvated by external CO molecules. Three CO stretching vibrational fundamentals were observed for the Fe(CO)(4)(-) core anion, indicating that the Fe(CO)(4)(-) anion has a C(3v) structure. All the carbonyl stretching frequencies of the Fe(CO)(n)(-) anion complexes are red-shifted with respect to those of the corresponding neutrals.     

Vibrational study and spectra-structure correlations in ammonium saccharinate: comparison with the alkali saccharinates

The FT IR spectra, at temperatures from liquid-nitrogen boiling (LNT) up to room temperature (RT), as well as the RT Raman solid-state spectra of protonated and deuterated ammonium saccharinate and of a series of alkali (Na, K, Rb, Cs) saccharinates are studied. The spectral assignments are aided with ab initio calculations on the free saccharinato anion at the HF/6-31 + + G(d,p) level. Attention is paid to the ND, CO and SO2 stretching regions. Correlation splitting is believed to be responsible for the presence of a v(CO) doublet. The averaged v(CO) frequency in (purely ionic) ammonium saccharinate is found to be the lowest in the so far studied saccharinates, along with the assumptions that the v(CO) frequency (or the corresponding averaged value) can have predictive value for the type of the metal-to-saccharinato ligand/ion bonding. The appreciably higher contribution of the dominating internal coordinate in the corresponding normal vibration in case of v(as)(SO2) than in v(s)(SO2) makes it suitable for spectra-structure correlations. Contrary to RT, even though no phase transitions were observed in the studied temperature range, some polycentered character is prescribed to the hydrogen bonds in which the ammonium ions of effective symmetry C8 participate at LNT. Certain structural predictions about the saccharinates of K, Rb and Cs are made.     

Experimental and theoretical vibrational study of bis(N,N-dimethylthiocarbamoylthio)acetic acid.

Harmonic vibrational analysis at HF/3-21G level is performed on the ab initio optimized molecular structure of bis(N,N-dimethylthiocarbamoylthio)acetic acid, and the outcome used in assigning the infrared spectrum of the acid. The calculated spectrum compares well with the experimental solid-state FT IR spectrum recorded at 298 and at 77 K.     

Reversible bromide-chloride exchange in zirconium cluster compounds: synthesis by means of ionic liquids, structures, and some spectral data of (EMIm)(4)[(Zr(6)Z)Br(18)] cluster phases (Z = Be, Fe)

The solid-state precursor cluster chlorides Na(4)[(Zr(6)Be)Cl(16)] and K[(Zr(6)Fe)Cl(15)] readily dissolve in Lewis-basic ionic liquids consisting of mixtures of EMIm-Br and AlBr(3) (EMIm: 1-ethyl-3-methyl-imidazolium) to give dark colored solutions. From these solutions, the cluster phases (EMIm)(4)[(Zr(6)Fe)Br(18)] (1) and (EMIm)(4)[(Zr(6)Be)Br(18)] (2) were obtained in acceptable yields. Crystallographic data of the isostructural phases are the following: monoclinic, P2(1)/c, Z = 2. The data for 1 follow: a = 10.5746(4) Angstrom, b = 22.6567(9) Angstrom, and c = 13.0260(5) Angstrom, beta = 111.279(2) degrees. The data for 2 follow: a = 10.574(2) Angstrom, b = 22.681(4) Angstrom, and c = 13.041(2) Angstrom, beta = 111.31(2) degrees. Compound 1 is the first detailed structurally characterized molecular Fe-centered zirconium bromide cluster phase. In the bromide based ionic liquid, a complete exchange of all the outer and inner chlorides by bromide takes place. Since the inverse reaction, the exchange of all bromides by chlorides, was reported before, this complete ligand exchange can be considered as reversible, with the equilibrium being largely determined by the free ligand concentration. The electronic spectra of a chloride supported cluster precursor in different ionic liquids were measured and analyzed.     

Native and unfolded cytochrome c--comparison of dynamics using 2D-IR vibrational echo spectroscopy

Unfolded vs native CO-coordinated horse heart cytochrome c (h-cyt c) and a heme axial methionine mutant cyt c552 from Hydrogenobacter thermophilus ( Ht-M61A) are studied by IR absorption spectroscopy and ultrafast 2D-IR vibrational echo spectroscopy of the CO stretching mode. The unfolding is induced by guanidinium hydrochloride (GuHCl). The CO IR absorption spectra for both h-cyt c and Ht-M61A shift to the red as the GuHCl concentration is increased through the concentration region over which unfolding occurs. The spectra for the unfolded state are substantially broader than the spectra for the native proteins. A plot of the CO peak position vs GuHCl concentration produces a sigmoidal curve that overlays the concentration-dependent circular dichroism (CD) data of the CO-coordinated forms of both Ht-M61A and h-cyt c within experimental error. The coincidence of the CO peak shift curve with the CD curves demonstrates that the CO vibrational frequency is sensitive to the structural changes induced by the denaturant. 2D-IR vibrational echo experiments are performed on native Ht-M61A and on the protein in low- and high-concentration GuHCl solutions. The 2D-IR vibrational echo is sensitive to the global protein structural dynamics on time scales from subpicosecond to greater than 100 ps through the change in the shape of the 2D spectrum with time (spectral diffusion). At the high GuHCl concentration (5.1 M), at which Ht-M61A is essentially fully denatured as judged by CD, a very large reduction in dynamics is observed compared to the native protein within the approximately 100 ps time window of the experiment. The results suggest the denatured protein may be in a glassy-like state involving hydrophobic collapse around the heme.     

The totally symmetric Raman stretching vibration v(Mo-Mo) of quadruple molybdenum–molybdenum bonds varies linearly with the mass of molybdenum and its ligands

The electronic (400-800nm), i.r. and Raman (20-400cm-1) spectra of several hexahalo-di(aquo)dimolybdate(II) anions, Mo2X6(H2O)22− (X=Cl, Cl/Br, Br and I) containing quadruple metal-metal bonds have been investigated. The electronic spectra of the solid compounds at 300K show intense bands in the visible region (510-580nm) assigned to the expected delta delta transitions. From the i.r. and Raman spectra the skeletal and stretching modes in these binuclear anions have been identified. The metal-metal v(MoMo) stretching vibrational wavenumbers vary linearly as a function of the total mass, including molybdenum and its ligands. From this relationship, the mass of the ligands and that of the unknown material have been determined and compared with analytical results. In conclusion, the results are in very good agreement. This revised version was published online in June 2006 with corrections to the Cover Date.     

Gold cluster carbonyls: vibrational spectroscopy of the anions and the effects of cluster size, charge, and coverage on the CO stretching frequency

We report the vibrational spectra of the carbonyl complexes of anionic gold clusters in the range of the CO stretching frequency as measured in the gas phase using IR multiple photon dissociation spectroscopy. The investigated complexes contain between 3 and 14 Au atoms and up to 7 CO ligands. Special attention is given to the complexes that exhibit saturation CO coverage as well as to the monocarbonyl species. In conjunction with data from the corresponding cationic complexes we quantify how the CO stretching frequency varies with the charge state of the gold cluster. Our results provide a size- and charge-dependent basis to interpret values of the CO stretching frequency measured for CO on deposited gold clusters in terms of the charge states of the clusters.     

C-H stretching vibrations of methyl, methylene and methine groups at the vapor/alcohol (N = 1-8) interfaces

In IR and Raman spectral studies, the congestion of the vibrational modes in the C-H stretching region between 2800 and 3000 cm(-1) has complicated spectral assignment, conformational analysis, and structural and dynamics studies, even with quite a few of the simplest molecules. To resolve these issues, polarized spectra measurement on a well aligned sample is generally required. Because the liquid interface is generally ordered and molecularly thin, and sum frequency generation vibrational spectroscopy (SFG-VS) is an intrinsically coherent polarization spectroscopy, SFG-VS can be used for discerning details in vibrational spectra of the interfacial molecules. Here we show that, from systematic molecular symmetry and SFG-VS polarization analysis, a set of polarization selection rules could be developed for explicit assignment of the SFG vibrational spectra of the C-H stretching modes. These polarization selection rules helped assignment of the SFG-VS spectra of vapor/alcohol (n = 1-8) interfaces with unprecedented details. Previous approach on assignment of these spectra relied on IR and Raman spectral assignment, and they were not able to give such detailed assignment of the SFG vibrational spectra. Sometimes inappropriate assignment was made, and consequently misleading conclusions on interfacial structure, conformation and even dynamics were reached. With these polarization rules in addition to knowledge from IR and Raman studies, new structural information and understanding of the molecular interactions at these interfaces were obtained, and some new spectral features for the C-H stretching modes were also identified. Generally speaking, these new features can be applied to IR and Raman spectroscopic studies in the condensed phase. Therefore, the advancement on vibrational spectra assignment may find broad applications in the related fields using IR and Raman as vibrational spectroscopic tools.     

Cr(CO)5(CNCN), a complex in which the coordinated CN group of isocyanogen binds and vibrates like a CO ligand

The IR and Raman spectra have been determined of the products formed by low-temperature (−20°C) replacement of 2-MeTHF (2-methyltetrahydrofuran) in photochemically produced Cr(CO)₅(2-MeTHF) by isocyanogen, CNCN. The IR spectra are interpreted in terms of the formation of an isonitrile and a nitrile complex, Cr(CO)₅(CNCN) and Cr(CO)₅(NCNC). A detailed study of the IR and Raman spectra of Cr(CO)₅(CNCN), which was formed in large excess, reveals that the coordinating CN group of CNCN has coordinating and vibrational properties almost identical to those of the CO ligands in this complex.