Upali A. Jayasooriya

Vibrational spectroscopic characterisation of hydrogen bridged between metal atoms: A model for the adsorption of hydrogen on low-index faces of tungsten

Abstract Vibrational spectra of hydrogen chemisorbed on metal surfaces are discussed in the context of data from model cluster compounds and adsorption sites for hydrogen on low index planes of tungsten are suggested on the basis of reported electron energy loss spectra. A hydrogen adsorption site bridging two metal atoms is proposed for both the low coverage, β 2 , and the high coverage, β 1 , states of hydrogen on W(100) and the change in the symmetric metal-hydrogen stretching frequency is correlated with the reconstruction of the tungsten surface in the β 2 state.

Uptake and Toxicity Studies of Poly-Acrylic Acid Functionalized Silicon Nanoparticles in Cultured Mammalian Cells

Poly-acrylic acid (PAAc) terminated silicon nanoparticles (SiNPs) have been synthesized and employed as a synchronous fluorescent signal indicator in a series of cultured mammalian cells: HHL5, HepG2 and 3T3-L1. Their biological effects on cell growth and proliferation in both human and mouse cell lines have been studied. There was no evidence of in vitro cytotoxity in the cells exposed to PAAc terminated SiNPS when assessed by cell morphology, cell proliferation and viability, and DNA damage assays. The uptake of the nanocrystals by both HepG2 and 3T3-L1 cells was investigated by confocal microscopy and flow cytometry, which showed a clear time-dependence at higher concentrations. Reconstructed 3-D confocal microscope images exhibited that the PAAc-SiNPs were evenly distributed throughout the cytosol rather than attached to outer membrane. This study provides fundamental evidence for the safe application and further modification of silicon nanoparticles, which could broaden their application as cell markers in living systems and in micelle encapsulated drug delivery systems.

A simultaneous FT-Raman–DSC (SRD) study of polymorphism in sn-1,3-distearoyl-2-oleoylglycerol (SOS)

The simultaneous FT-Raman–differential scanning calorimetry (SRD) technique is described, which allows FT-Raman spectra to be collected from thermally sensitive samples with a very low power density at the sample surface, immediately followed by an in situ DSC melting curve. This gives unambiguous characterisation of samples which are thermally sensitive or which could be structurally transformed by an incident high power density laser beam. In the current work, SRD has been applied to a study of the structural polymorphs of the triglyceride 1,3-distearoyl-2-oleoylglycerol (SOS). SRD analysis shows DSC heating curves with onset melting points and features identifying the polymorphs produced as α, γ, β′, β2 and β1, conforming well to literature thermal behaviour. Interpretation of the corresponding Raman spectra for these polymorphs provides confirmation of existing structural models in the literature based on other analytical techniques.

The vibrational spectrum of solid ferrocene by inelastic neutron scattering

We calculate the spectrum of internal vibrations of a single ferrocene Fe(C5H5)2 molecule using ab initio density functional theory (without free parameters) and compare this with inelastic neutron scattering data on ferrocene in the solid state at 28 K. Due to the good agreement, we can assign each vibrational mode to each observed peak in the neutron spectrum and so remove ambiguities existing in the literature. There is also consistency between the calculated potential energy of a single ferrocene molecule for different orientations, φ, of the two cyclopentadienyl C5H5 rings with respect to each other, which shows a potential barrier of 0.9 kcal/mol, and electron diffraction, and between the calculated shallow minimum at φ=9 deg and x-ray diffraction.

Introduction to Raman Spectroscopy

Raman spectroscopy is the study of inelastic scattering of light. The inelasticity stems from a transfer of energy between the incident radiation field and the material under investigation. The technique provides, amongst other things, important information about the vibrational state of matter. One of the most influential early investigations into light scattering was undertaken by Lord Rayleigh (1899). In this study it was shown that the intensity of elastically scattered light is strongly dependent on its wavelength. In fact an inverse fourth power dependence on wavelength was proved, and was subsequently called the Rayleigh law. The process of inelastic scattering was theoretically predicted by Brillouin (1922) and Smekal (1923). (In Brillouin scattering radiation couples with acoustic modes of a system.) Key observations of very weak inelastic scattering phenomena were made in a remarkable experiment undertaken by C. V. Raman together with K. S. Krishnan (1928). The experimental set-up comprised focussed, filtered sunlight as the source, a sample of neat liquid and a telescope as the detector. Soon after, Landsberg and Mandelstam (1928) reported inelastic scattering of light from quartz with Cabannes (1928), Rocard (1928), and Raman and Krishnan (1929) themselves also offering subsequent quantitative studies in various media. Several books provide excellent descriptions of the history of the Raman effect (Long, 1977; Ferraro and Nakamoto, 1994).

Simultaneous FT-Raman Differential Scanning Calorimetry Measurements Using a Low-Cost Fiber-Optic Probe

A low-cost fiber-optic probe was constructed and used to couple an FT-Raman spectrometer to a differential scanning calorimeter (DSC). The utility of this system is demonstrated by the investigation of the different phases of ammonium nitrate.

Vibrational spectra of carboxylato complexes—VI. Isotopic substitution in the mixed-metal trinuclear complexes [FeIII2NiIIO(OOCCH3)6L3]

Abstract Infrared and Raman spectra of the complexes [Fe III 2 Ni II O(OOCCH 3 ) 6 L 3 ], L = C 5 H 5 N and H 2 O, are reported. Assignments in the region 800 to 200 cm −1 are made on the basis of substitution of 18 O for 16 O (central oxygen) and deuteration. In particular, the two components of the in-plane asymmetric vibration ν as (Fe 2 NiO) are identified at 722 and 565 cm −1 .

The M–H bond stretching frequencies of µ2-bridged metal hydrides and their relationship to the M–H–M interbond angle

A successful theoretical correlation is made of experimental data on the M–H bond stretching modes of µ2-bridged metal hydrides with the M–H–M interbond angle, based on the application of central or valence force field to the MHM unit.

Molecular dynamics of organometallic compounds using μSR

The potential of μSR in the investigation of molecular dynamics of organometallic compounds is illustrated with applications to the classic metallocene compound, ferrocene. Muonium addition gives two radicals in this case with the slowly relaxing radical showing a repolarisation curve corresponding to a hyperfine field of ca. 200 G suggesting addition to the cyclopentadienyl ring. The temperature dependence of the relaxation of this radical gives an activation energy of ca. 5.4 kJ/mol, in good agreement with QENS and NMR estimates for cyclopentadienyl, ring rotation in this compound.

Exchange interactions in trinuclear basic chromium(III) clusters : direct observation of the magnetic spectrum by inelastic neutron scattering

Incoherent inelastic neutron scattering spectra are reported for salts of the complex [Cr3O(OOCCH3)6(OH2)3]+. The data are consistent with predominantly antiferromagnetic coupling between pairs of chromium ions. The complete spectrum of transitions between successive states with total spin S=1/2, 3/2, 5/2, 7/2, and 9/2 has been observed for the first time. Splittings of the ground state S=1/2 have been observed directly and attributed to lowering of symmetry of the triangular cluster. For the chloride salt the data confirm that two sets of complex cations with different degrees of symmetry lowering are present in the crystal, at least at the lowest temperatures used (T=1.4 to 50 K). In principle, the relationship of J values for the symmetry‐lowered case could be described as ‘‘isosceles,’’ with Jab≳Jbc=Jac or Jab<Jbc=Jac; or as ‘‘scalene,’’ with all three J values different. We find that, for at least one of the two sets of metal ion clusters, the scalene case applies, with J values of −11.5±0.2, −10.5±0...