Coherent Raman spectra of the nu1 mode of carbon suboxide

High-resolution (0.001 cm(-1)) coherent anti-Stokes Raman spectroscopy (CARS) has been used to study the nu1 symmetric CO stretching mode of the quasi-linear molecule carbon suboxide, C3O2. Q-branch transitions are seen that originate from the ground state and from thermally populated levels of the nu7 CCC bending mode, which is of unusually low frequency. The intensity variation of the Q-branch features on cooling to about 120 K in a jet expansion requires the reversal of the order of assignment given in a previous Raman study at low resolution. The identification of the nu1 sigma(g)+ <-- sigma(g)+ transition from the ground state is confirmed by the absence of J(odd) Q-branch lines in the resolved CARS spectrum. Analysis of this band in terms of a quasi-linear model gives a good fit to the observed transitions and leads to vibrational-rotational parameters (in cm(-1)) of nu1 = 2199.9773(12) and (B' - B') = -2.044(6) x 10(-4). Other transitions originating from higher nu7 levels occur at only slightly lower wavenumber values and permit the calculation of the double minimum potential in the Q7 bending coordinate. The results indicate that the ground-state barrier to linearity (21.5 cm(-1)) increases by only 0.6 cm(-1) when the CO symmetric stretch is excited.     

Axial ligand substituted nonheme FeIV=O complexes: observation of near-UV LMCT bands and Fe=O Raman vibrations

Axial ligand substitution of a mononuclear nonheme oxoiron(IV) complex, [FeIV(O)(TMC)(NCCH3)]2+ (1) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), leads to the formation of new FeIV=O species with relatively intense electronic absorption features in the near-UV region. The presence of these near-UV features allowed us to make the first observation of Fe=O vibrations of S = 1 mononuclear nonheme oxoiron(IV) complexes by resonance Raman spectroscopy. We have also demonstrated that the reactivity of nonheme oxoiron(IV) intermediates is markedly influenced by the axial ligands.     

The nu1 CH stretching mode of the ketenyl (HCCO) radical

The nu(1) CH stretch, a previously uncharacterized mode of the ketenyl (HCCO) radical, has been identified at 3232 cm(-1) through time-resolved Fourier transform infrared emission spectroscopy of rovibrationally excited ketenyl generated, along with ethyl (CH(2)CH(3)), with near-unit quantum efficiency via the 193 nm photodissociation of ethyl ethynyl ether. IR emission from the vibrationally excited photoproducts was detected with both temporal and frequency resolutions. Spectral assignments were supported by comparison with theoretical calculations as well as two-dimensional correlation analysis.     

Raman spectrum of supercritical C(18)O2 and re-evaluation of the Fermi resonance

We report the first Raman spectra of fully (18)O-labeled supercritical CO(2) (scCO(2)) and various isotopic mixtures. The experimental results, coupled with ab initio molecular dynamics calculations, demonstrate that the frequencies assigned to the Fermi dyad of the CO(2) molecule transpose upon isotopic labeling of both oxygen atoms. Although the transposition of the Fermi dyad of CO(2) gas due to isotopic substitution has been discussed before, this is the first confirmation of the effect in the Raman spectrum of the supercritical fluid and provides necessary groundwork for future Raman spectroscopy studies of reactions in this important medium. More importantly, the work yields a quantitative assessment of the mixing of states upon labeling that provides the needed clarification concerning the pedigree of the assignments for the dyad of CO(2) under supercritical conditions.     

Efficient vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF4

A laser flash photolysis-laser-induced fluorescence (LIF) technique has been employed to study the relaxation kinetics of vibrationally excited O2(X 3sigma(g)-. The time-resolved LIF excited B 3sigma(u)(-)-X 3sigma(g)- system has been recorded and analyzed by the integrated-profiles method. The rate coefficient for vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF(4), [1.4 +/- 0.3(2sigma)] x 10(-11) cm3 molecule(-1) s(-1), indicates that CF4 is an efficient relaxant of O2(X 3sigma(g)- and that the propensity rule for O2 relaxation suggested by Mack et al. (J. A. Mack, K. Mikulecky and A. M. Wodtke, J. Chem. Phys., 1996, 105, 4105) has been observed experimentally.     

Monodisperse MFe2O4 (M = Fe, Co, Mn) nanoparticles

High-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)(3), with 1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite (Fe(3)O(4)) nanoparticles. Similarly, reaction of Fe(acac)(3) and Co(acac)(2) or Mn(acac)(2) with the same diol results in monodisperse CoFe(2)O(4) or MnFe(2)O(4) nanoparticles. Particle diameter can be tuned from 3 to 20 nm by varying reaction conditions or by seed-mediated growth. The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD. Further, Fe(3)O(4) can be oxidized to Fe(2)O(3), as evidenced by XRD, NEXAFS spectroscopy, and SQUID magnetometry. The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made. These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.     

Resonance Raman studies of HOO-Co(III)bleomycin and Co(III)bleomycin: identification of two important vibrational modes, nu(Co-OOH) and nu(O-OH)

Bleomycin is an antitumor agent whose cytotoxicity is dependent on its ability to bind DNA in the nucleus and effect double-stranded DNA cleavage, which is difficult for the cell to repair. In order for this DNA cleavage to occur, bleomycin must, through a series of reactions, form a low-spin Fe(III) complex, the putative "activated" form of the drug, HOO-Fe(III)bleomycin. The relative strengths of the bonds in the Fe(III)-OOH linkage have not been determined due to the weakness of the hydroperoxo-to-iron(III) charge-transfer transition. The much more stable HOO-Co(III)bleomycin has often been studied as a structural analogue of HOO-Fe(III)bleomycin, and hence, an understanding of the relative bond strengths in the Co-OOH linkage may serve to enhance our understanding of the analogous Fe-OOH linkage. In this report, we present resonance Raman data that identify two important vibrational modes in the Co-OOH linkage, the stretching modes, nu(Co-OOH) and nu(O-OH). Both of these vibrational modes were found to be unperturbed by complexation of the drug with calf thymus DNA. Advantage was also taken of the isostructural realtionship between Fe-bleomycin and Co-bleomycin to analyze and assign the high-frequency modes for HOO-Co(III)bleomycin and Co(III)bleomycin (A(2) and B(2)). These data could be useful for future studies of photoactivated Co-bleomycin and Co-bleomycin analogues in an attempt to characterize oxygen-independent DNA damage pathways.     

Solvent dependent analysis of isotropic Raman band shape of C=O stretching vibration

The isotropic Raman band shape corresponding to C=O stretching vibration of some molecules has been studied in neat liquids and as a function of solvent concentration using both polar and non-polar solvents. The Raman band shape was analyzed on the basis of correlation with the Lorentzian line shape by employinga simple method of linear curve fitting. In neat liquids and in low solvent concentration region, the band shape was found to be non-Lorentzian. With the gradual increase in solvent concentration the band shape approaches a Lorentzian function. The plot of the correlation coefficient for a Lorentzian shape shows a discontinuity in the intermediate range of solvent concentration. The influence of the structural characteristics of the solute and the solvent systems on the reference mode and various multipolar interactions together with the time varying spatial distribution of solvent molecules with respect to the reference molecule are expected to govern the microenvironmental fluctuations. This may be responsible for the discontinuity in the intermediate solvent concentration region.     

Fermi resonance at the P=O group frequency

Conclusions Fermi resonance is the factor principally responsible for band multiplicity in P=O group stretching vibrations in diethyl ethylphosphonate ( _P=O). Parameters have been determined for the resonating and unperturbed levels.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No, 9, pp. 1987–1991, September, 1977.The authors wish to thank V. A. Kharlamov who furnished the DEEP used here.     

Fragmentary analysis of crystal structures of the Al,Ca-ferrite phase (Fe,Ca)4(Fe,Al)2CaFe(Al,Fe)2O14

The crystal structure of a somatic compound, Ca_7.12Fe_24.7Al_8.18O₅₆, is investigated by isolating spinel (Fe₃O₄) and pyroxene [Ca(Fe, Ca)(Al, Si)₂O₆] parent structures (fragments) from the homogeneous region of the Al, Ca-ferrite (CFA) phase. Crystal chemical factors leading to formation of these fragments and conditions for their conjugation are revealed. Polytypic modifications and structural homologs of the CFA phase are considered. It is suggested that somatic (fragmentary) structures be analyzed by determining an n-dimensional periodic fragment of the parent structure, isolating a subset of fragmentary structures from modular ones, and establishing common features of parent structure fragments in derivative fragmentary structures. Admissible chemical compositions of the CFA phase are analyzed; the role of the Si impurity in stabilizing structural homologs of the CFA phase is discussed. Baikov Institute of Metallurgy, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 5, pp. 84–96, September–October, 1994. Translated by L. Smolina     

Discovery of C(60)O(3) isomer having C(3)(nu) symmetry

A hitherto undetected type of C(60)O(3) isomer was found in the reaction solution of C(60) with m-chloroperoxybenzoic acid by means of a chromatographic technique using two different columns. Both electronic spectroscopy and atmospheric pressure chemical ionization (APCI) mass-spectroscopy examinations show its C(3)(nu) symmetry, in which three oxygen atoms are added onto one benzenoid ring of C(60).     

Three banana-shaped arsenomolybdates encapsulating a hexanuclear transition-metal central magnetic cluster: [As(III)2Fe(III)5MMo22O85(H2O)]n- (M = Fe3+, n = 14; M = Ni2+ and Mn2+, n = 15)

Three polyoxometalates encapsulating high-nuclearity magnetic clusters MFe(5), [As(2)MFe(5)Mo(22)O(85)(H(2)O)](n-) (M = Fe(3+), n = 14; M = Ni(2+) and Mn(2+), n = 15), were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetric analysis, and magnetism measurements. The polyanion [As(2)MFe(5)Mo(22)O(85)(H(2)O)](n-) consists of a central MMo(7)O(28) (M = Fe(3+), Ni(2+), and Mn(2+)) fragment and two AsMo(7)O(27) fragments linked together by two trimeric clusters, Fe(2)MoO(μ(2)-O)(2) and Fe(3)(H(2)O), to form a banana-shaped structure with C(1) symmetry. The MMo(7)O(28) and AsMo(7)O(27) units have a similar structure and can be considered as a monocapped hexavacant α-B-Keggin subunit with a central MO(4) group or a central As(III)O(3) group. The polyoxometalates have a low absorption of υ(Mo-O(d)) (925-913 cm(-1)) because most of the Mo atoms in the polyanions have at least two longer Mo-O(d) bonds. The framework of the arsenomolybdates is stable before As(2)O(3) escaping (ca. 300 °C). The analysis of magnetostructural correlations and magnetism measurements indicate the coexistence of ferro- and antiferromagnetic interactions, which give an overall ferromagnetic spin ground state in the compounds.     

New results for the OH (nu = 0,j = 0) + CO (nu = 0,j = 0) --> H + CO2 reaction: Five- and full-dimensional quantum dynamical study on several potential energy surfaces

Full- [six-dimensional (6-D)] and reduced-dimensional [five-dimensional (5-D)] quantum wave packet calculations have been performed for the title reaction to obtain reaction probabilities deriving from the ground rovibrational states of OH and CO with total angular momentum J = 0. Three potential energy surfaces (PES) are studied, namely, those of Bradley and Schatz (BS), Yu, Muckerman, and Sears (YMS), and Lakin, Troya, Schatz, and Harding (LTSH). 6-D calculations are performed only for the BS PES, while 5-D results are reported for all three PES'. The 6-D results obtained in the present work improve on those previously reported, since a larger vibrational basis and a better representation of the OH and CO bonds has been introduced. In particular, we now employ a generalized Lanczos-Morse discrete variable representation for both the OH and CO vibrations. In a further improvement, the generalized discrete variable representation of the CO vibration is based on different CO intramolecular potentials for the asymptotic and product grids employed in our projection formalism. This new treatment of the vibrational bases allows for a large reduction in computation time with respect to our previous implementation of the wave packet method, for a given level of accuracy. As a result, we have been able to extend the range of collision energies for which we can obtain converged 6-D results to a higher energy (0.8 eV) than was possible before (0.5 eV). The comparison of the new 6-D and previous 5-D results for the BS PES shows good agreement of the general trend in the reaction probabilities over all collision energies considered (0.1-0.8 eV), while our previous 6-D calculation showed reaction probabilities that differed from the 5-D results by up to 10% between 0.5 and 0.8 eV. The 5-D reaction probabilities reveal interesting trends for the different PES'. In particular, at low energies (< 0.2 eV) the LTSH PES gives rise to much larger reactivity than the other PES', while at high energies (> 0.3 eV) its reaction probability decreases with respect to the BS and YMS PES', being more than a factor of 2 smaller at 0.8 eV. A 5-D calculation on a modified version of the LTSH surface shows that the van der Waals interaction in the entrance channel, which is not correctly described in the other PES' is largely responsible for its larger reactivity at low energies. The large difference between the 5-D reaction probabilities for the YMS and LTSH PES' serves to emphasize the importance of the van der Waals interaction for the reactivity at low energies, because most of the stationary point energies on the YMS and LTSH PES are rather similar, being in line with high-level ab initio information.     

Non-adiabatic interaction and the resonance Raman scattering for a non-totally symmetric mode

It is shown that the inclusion of the non-adiabatic interaction between two electronic states distorts the mirror symmetry of the excitation spectrum and depolarization dispersion for resonance Raman scattering in the region of the 00 and the 01 band of the resonating excited electronic state.     

Rotationally selected product pair correlation in F+CD(4)-->DF(nu('))+CD(3)(nu=0,N)

The title reaction was studied in a crossed-beam experiment by imaging of state-selected products. The rotational state selection of the CD(3) products was achieved using (2+1) resonance-enhanced multiphoton ionization. The coincident information on the DF coproducts was revealed in a state-resolved manner from time-sliced velocity map images. Significant dependences of both the correlated differential cross sections and the DF vibrational branching ratios on the "tagged" CD(3) rotation states were found. The dynamical implications of one of the major findings are discussed.     

Crystal structure and heat capacity of the mixed-valence trinuclear iron monoiodoacetate complex, [Fe(III)2Fe(II)O(O2CCH2I)6(H2O)3][Fe(III)3O(O2CCH2I)6(H2O)3]I

The crystal structure of a trinuclear iron monoiodoacetate complex was determined. Although it has been incorrectly characterized as [Fe₃O(O₂CCH₂I)₆(H₂O)₃], the correct chemical formula turned out to be [Fe(III)₂Fe(II)O(O₂CCH₂I)₆(H₂O)₃]-[Fe(III)₃O(O₂CCH₂I)₆(H₂O)₃]I (1). The two kinds of Fe₃O molecules (Fe(III)₂Fe(II)O and Fe(III)₃O) are crystallographically indistinguishable. All the Fe atoms are crystallographically equivalent because of a crystallographic threefold symmetry. Heat capacities of 1 seem to exhibit no thermal anomaly in the temperature range 5.5–309 K, although the valence detrapping phenomenon has been observed in this temperature range. This fact indicates that the valence-detrapping phenomenon in 1 occurs without any phase transition, leading 1 to a glassy state, probably because the crystal of 1 is just like a solid solution of distorted mixed-valence Fe(III)₂Fe(II)O molecules and permanently undistorted Fe(III)₃O molecules which may act as an inhibitor for a cooperative valence-trapping.     

Magnetic Characteristics of Trinuclear Complexes [M3O(CH3COO)6(pz)3]+ (M = Fe,Cr; pz = Pyrazine)

Conditions were found for the synthesis of new trinuclear carboxylates [M₃O(CH₃COO)₆(pz)₃]⁺ (M = Fe, Cr; pz = pyrazine). The composition of the obtained complexes was established on the basis of elemental analysis, mass spectrometry, and electronic and IR spectroscopy. It was shown that the substitution of water molecules by pyrazine leads to some increase in the antiferromagnetic exchange between the metal ions of the trinuclear cation. It was established that spin frustration exists in the complexes.     

Magnetic properties of complex oxides Gd2SrM2O7 (M = Fe, Al)

Magnetic susceptibility of complex perovskite-like oxides Gd₂SrFe₂O₇ and Gd₂SrAl₂O₇ was studied. A sharp decrease in the magnetic characteristics of gadolinium ferrite as compared to gadolinium aluminate points to the presence of strong antiferromagnetic interactions between the iron ions.     

Normal mode analysis of Pyrococcus furiosus rubredoxin via nuclear resonance vibrational spectroscopy (NRVS) and resonance raman spectroscopy

We have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the Fe(S(cys))(4) site in reduced and oxidized rubredoxin (Rd) from Pyrococcus furiosus (Pf). The oxidized form has also been investigated by resonance Raman spectroscopy. In the oxidized Rd NRVS, strong asymmetric Fe-S stretching modes are observed between 355 and 375 cm(-1); upon reduction these modes shift to 300-320 cm(-1). This is the first observation of Fe-S stretching modes in a reduced Rd. The peak in S-Fe-S bend mode intensity is at approximately 150 cm(-1) for the oxidized protein and only slightly lower in the reduced case. A third band occurs near 70 cm(-1) for both samples; this is assigned primarily as a collective motion of entire cysteine residues with respect to the central Fe. The (57)Fe partial vibrational density of states (PVDOS) were interpreted by normal mode analysis with optimization of Urey-Bradley force fields. The three main bands were qualitatively reproduced using a D(2)(d) Fe(SC)(4) model. A C(1) Fe(SCC)(4) model based on crystallographic coordinates was then used to simulate the splitting of the asymmetric stretching band into at least 3 components. Finally, a model employing complete cysteines and 2 additional neighboring atoms was used to reproduce the detailed structure of the PVDOS in the Fe-S stretch region. These results confirm the delocalization of the dynamic properties of the redox-active Fe site. Depending on the molecular model employed, the force constant K(Fe-S) for Fe-S stretching modes ranged from 1.24 to 1.32 mdyn/A. K(Fe-S) is clearly diminished in reduced Rd; values from approximately 0.89 to 1.00 mdyn/A were derived from different models. In contrast, in the final models the force constants for S-Fe-S bending motion, H(S-Fe-S), were 0.18 mdyn/A for oxidized Rd and 0.15 mdyn/A for reduced Rd. The NRVS technique demonstrates great promise for the observation and quantitative interpretation of the dynamical properties of Fe-S proteins.