Isomer discrimination of polycyclic aromatic hydrocarbons in the Murchison meteorite by resonant ionization

We have used two-color resonant two-photon ionization (2C-R2PI) mass spectrometry to discriminate between isomers of polycyclic aromatic hydrocarbons in the Murchison meteorite. We measured the 2C-R2PI spectra of chrysene and triphenylene seeded in a supersonic jet by laser desorption. Since each isomer differs in its R2PI spectrum, we can distinguish between isomers using wavelength dependent ionization and mass spectrometry. We found both chrysene and triphenylene in sublimates from carbonaceous residue obtained by acid demineralization of the Murchison meteorite. Their R2PI mass spectra show only the molecular ion, even though these samples contain a complex inventory of organic molecules.     

On the origin of the Murchison meteorite phosphonates. Implications for pre-biotic chemistry

Ab initio calculations, combined with experimental studies on the anaerobic hydrolysis of phosphaalkynes under thermal and photochemical conditions suggest a potential, exogenous source of reduced oxidation state phosphorus for the early Earth.     

On the characterization of disordered and heterogeneous carbonaceous materials by Raman spectroscopy

The applicability of Raman spectroscopy to characterize disordered and heterogeneous carbonaceous materials (CM) is discussed, by considering both natural and synthetic CM. First, different analytical mismatches during the measurement are discussed and technical indications are provided in order to eliminate them. Second, the accuracy and relevance of the different parameters obtained by the decomposition of spectra by conventional fitting procedure, is reviewed. Lastly, a new Raman technique (Raman area mode microspectroscopy) giving an homogeneous repartition of power within a large laser beam is presented, this technique being powerful to study strongly heterogeneous CM and/or photosensitive samples.     

Measurement of the carbonaceous component in the Milan urban particulate matter

The carbonaceous component in the Milan urban particulate matter, i.e. the two components black carbon (BC) and organic carbon (OC), has been measured by means of a thermogravimetric analyzer combined with an infrared spectrophotometer (TGA/FT-IR). While black carbon may be considered a primary pollutant, organic carbon includes both primary emissions and secondary organic aerosols. Since carbonaceous aerosol (including a small quantity of inorganic carbon, too) makes up roughly from 25% to 50% of the average annual PM 2.5 mass concentration, a deeper understanding of this component is required. The TGA/FT-IR technique, employed for the first time to our knowledge for the quantification of the particulate matter carbonaceous component, allows, thought the results here presented are preliminary, to assess the two components BC and OC in a simple way especially if compared with the methods reported in the literature. The total carbon (TC) determinations performed by TGA/FT-IR on Milan urban particulate matter are in good agreement with the results obtained by a total organic carbon (TOC) analyzer operating directly on the solid sample.     

Photodissociation dynamics of the ethoxy radical investigated by photofragment coincidence imaging

The photodissociation dynamics of the ethoxy radical (CH3CH2O) have been studied at energies from 5.17 to 5.96 eV using photofragment coincidence imaging. The upper state of the electronic transition excited at these energies is assigned to the C2A'state on the basis of electronic structure calculations. Fragment mass distributions show two photodissociation channels, OH + C2H4 and CH3 + CH2O. The presence of an additional photodissociation channel, identified as D + C2D4O, is revealed in time-of-flight distributions from the photodissociation of CD3CD2O. The product branching ratios and fragment translational energy distributions for all of the observed mass channels are nonstatistical. Moreover, the significant yield of OH + C2H4 product suggests that the mechanism for this channel involves isomerization on the excited-state surface. Photodissociation at a much lower yield is seen following excitation at 3.91 eV, corresponding to a vibronic band of the B2A' <-- X2A' transition.     

Source apportionment of atmospheric carbonaceous particulate matter based on the radiocarbon

A method was established to quantitatively estimate sources of atmospheric carbonaceous matter, using a combination of radiocarbon technology, linear regression of organic carbon (OC) -K⁺ and elemental carbon (EC) tracer method. Fractional contributions of fossil fuels, biomass burning, biogenic secondary organic carbon (BSOC) and soil dust to the atmospheric size-resolved carbonaceous matters in Shanghai suburb were estimated using this new method. The fossil carbon contributed most of the OC in particles smaller than 0.49 μm, and its fraction decreased with the increase of particle size. Biomass burning contributed 17–28 % to the OC. The BSOC contributed comparable proportions to the OC in particles smaller than 3.0 μm with the biomass burning, but larger in the particles lager than 3.0 μm. The soil dust contributed least fraction to the OC of each size with a proportion of 2–13 %. The biomass burning and fossil sources shared comparable fraction of the EC in all size range.     

The adsorption of rifampicin on gold or silver surfaces mediated by 2-mercaptoethanol investigated by surface-enhanced Raman scattering spectroscopy

In this work the adsorption of the antibiotic rifampicin (RP) on the surface of gold (AuNP) or silver nanoparticles (AgNP) was investigated using both surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) spectroscopies. Such spectra were obtained in the absence and presence of the surface modifier 2-mercaptoethanol (ME) using excitations by laser radiations of 532, 632.8 and 1064 nm wavelengths. The use of different conditions under the presence of ME led to changes in the spectral pattern ascribed to the influence of resonance Raman (RR) effect and distinct chemical interactions of RP with the metallic surfaces. The sensibility of the chromophoric moiety, i.e. a <pi>-conjugated orbital, to the adsorption geometries, which can be controlled by surface modifiers, impacts the RR effect. Theoretical models involving RP and metal atoms were obtained from Density Functional Theory (DFT) calculations, and used for supporting the vibrational assignment.     

Reversible phase transformation of MnO2 nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy

The reversible phase transformation is reported from hexagonal to monoclinic structure responding to the intercalation/deintercalation of Na(+) between MnO(2) nanosheets upon potential cycling in aqueous electrolyte via an in situ Raman technique. This structural evolution will influence the Na(+) diffusion process in MnO(2) nanosheets and cause phase retention during the self-discharge process.     

The binding and correlation effects in carbon dioxide as investigated by gas X-ray diffraction

The X-ray scattering intensities of gaseous carbon dioxide have been measured by the enerey-dispersive method. Comparison of the measured intensities with theoretical calculations by the Hartree-Fock independent-atom model revealed the binding effect in the small-s region, which is largely consistent with theoretical predictions based on the molecular Hartree-Fock wavefunction.     

Source apportionment of carbonaceous particulate matter during haze days in Shanghai based on the radiocarbon

To estimate the sources of carbonaceous particulate matter, ¹⁴C and biomass-burning marker (levoglucosan) were measured in the form of organic carbon (OC) and elemental carbon (EC) in PM_2.5 that was collected in five different functional districts of Shanghai during winter 2013. Spatial variations of the contemporary proportion among different districts were evident. The results of levoglucosan in Xujiahui (XH) and Chongming (CM) agreed well with those of ¹⁴C. The results indicate that environmental protection policies should vary for functional districts within the same city to account for their different sources of emissions.     

The photodissociation dynamics of the ethyl radical, C2H5, investigated by velocity map imaging

The photodissociation dynamics of the ethyl radical C(2)H(5) has been investigated by velocity map imaging. Ethyl was produced by flash pyrolysis from n-propyl nitrite and excited to the A? (2)A(') (3s) Rydberg state around 250 nm. The energetically most favorable reaction channel in this wavelength region is dissociation to C(2)H(4) (ethene) + H. The H-atom dissociation products were ionized in a [1+1(')] process via the 1s-2p transition. The observed translational energy distribution is bimodal: A contribution of slow H-atoms with an isotropic angular distribution peaks at low translational energies. An expectation value for the fraction of excess energy released into translation of = 0.19 is derived from the data, typical for statistical dissociation reactions. In addition, a fast H-atom channel is observed, peaking around 1.8 eV. The latter shows an anisotropic distribution with β = 0.45. It originates from a direct dissociation process within less than a rotational period. Time-delay scans with varying extraction voltages indicate the presence of two rates for the formation of H-atoms. One rate with a sub-nanosecond time constant is associated with H-atoms with large translational energy; a second one with a time constant on the order of 100 ns is associated with H-atoms formed with low translational energy. The data confirm and extend those from previous experiments and remove some inconsistencies. Possible mechanisms for the dissociation are discussed in light of the new results as well as previous ones.     

The structure of water in polymer systems as revealed by Raman spectroscopy

A review on the structure of water in aqueous polymer systems as revealed by Raman spectroscopy is presented. Various interpretations and analysis procedures for Raman bands of liquid water which have been proposed are introduced. The structure and hydrogen-bonding properties of water which exist in aqueous polymer solutions and gels are described. Effects of chemical properties of polymer chains and size of water domains surrounded by polymer chains on the structure of water are discussed.     

Time-evolution of the entropy of fluctuations in some biological systems as investigated by NMR

A simple expression for the entropy of fluctuations has been developed, using the tunnelling-effect model. This gives the possibility to estimate the changes and evolution to entropy in non-crystalline and biological samples by NMR investigations. On the other hand, the oscillatory character of the time-evolution of some properties, experimentally found in the investigated samples of plants, is interpreted in terms of the generalized master equation with an exponential memory function.     

CW- and pulsed-EPR of carbonaceous matter in primitive meteorites: solving a lineshape paradox

Insoluble organic matter (IOM) of Orgueil and Tagish Lake meteorites are studied by CW-EPR and pulsed-EPR spectroscopies. The EPR line is due to polycyclic paramagnetic moieties concentrated in defect-rich regions of the IOM, with concentrations of the order of 4x10(19) spin/g. CW-EPR reveals two types of paramagnetic defects: centres with S=1/2, and centres with S=0 ground state and thermally accessible triple state S=1. In spite of the Lorentzian shape of the EPR and its narrowing upon increasing the spin concentration, the EPR line is not in the exchange narrowing regime as previously deduced from multi-frequency CW-EPR [L. Binet, D. Gourier, Appl. Magn. Reson. 30 (2006) 207-231]. It is inhomogeneously broadened as demonstrated by the presence of nuclear modulations in the spin-echo decay. The line narrowing, similar to an exchange narrowing effect, is the result of an increasing contribution of the narrow line of the triplet state centres in addition to the broader line of doublet states. Hyperfine sublevel correlation spectroscopy (HYSCORE) of hydrogen and (13)C nuclei indicates that IOM* centres are small polycyclic moieties that are moderately branched with aliphatic chains, as shown by the presence of aromatic hydrogen atoms. On the contrary the lack of such aromatic hydrogen in triplet states suggests that these radicals are most probably highly branched. Paramagnetic centres are considerably enriched in deuterium, with D/H approximately 1.5+/-0.5x10(-2) of the order of values existing in interstellar medium.     

The classification of mixed-valence complexes as deduced by resonance Raman spectroscopy

The basis of the static model for the classification of mixed-valence complexes is outlined. The resonance Raman spectra of a variety of mixed-valence complexes are described, and it is shown how these spectra may be used to differentiate between certain classes of mixed-valence complex.     

Spectroscopic analysis of L-histidine adsorbed on gold and silver nanoparticle surfaces investigated by surface-enhanced Raman scattering

The adsorption of l-histidine on gold (Au) and silver (Ag) nanoparticle surfaces has been comparatively analyzed by means of surface-enhanced Raman scattering (SERS). The SERS spectra of l-histidine on Ag were found to be quite different from those on Au, indicating dissimilar adsorption structures depending on metal substrates. Most peaks of l-histidine on Ag appeared to be due to coordination via the carboxylate (COO(-)) group with an imidazole ring of fairly upright geometry, whereas on Au it was assumed to adsorb with a rather flat geometry. A density functional theory (DFT) calculation was performed at the level of B3LYP/LANL2DZ to estimate the energetic stability of the binding of the imidazole ring and the carboxylate group of l-histidine with the Ag and Au atoms, respectively. Based on the DFT calculation, the carboxylate group of l-histidine was predicted to bind more favorably to Ag than to Au, and this was in line with our SERS spectral analysis.     

The association in mixtures of dimethylsulphoxide and water as studied by Raman spectroscopy

In mixtures of dimethylsulphoxide (DMSO) and water, formation of a complex (DMSO) · (H₂O)₂ is indicated by wavenumber shifts and linewidth variations of the v SO Raman band. Higher temperatures interfere with this complex formation.