Search results for "RAMAN"
showing 10 items of 1328 documents
Advanced piezoresistive sensor achieved by amphiphilic nanointerfaces of graphene oxide and biodegradable polymer blends
2018
This work focuses on the preparation of a piezoresistive sensor device, by exploiting an amphiphilic sample of graphene oxide (GO) as a compatibilizer for poly (lactic acid) (PLA)-Poly (ethylene-glycol) (PEG) blends. The presence of GO determined a high stiffening and strengthening effect, without affecting toughness, and allowed a good stability of mechanical properties up to 40 days. Moreover, GO endowed the materials with electrical properties highly sensitive to pressure and strain variations: the biodegradable pressure sensor showed a responsivity of 35 μA/MPa from 0.6 to 8.5 MPa, a responsivity around 19 μA/MPa from 8.5 to 25 MPa. For lower pressure values (around 0.16–0.45 MPa), inst…
Alternating, all-trans polyenynes: Model compounds for poly(diacetylene)s with defined conjugation length
1994
The syntheses of polyenynes as model compounds for poly(diacetylene)s (PDAs) are described. Variation of properties (UV–VIS, Raman, NMR and bond geometries) as a function of the chain length was investigated. After extrapolation to infinite chain length these data were compared to those for PDAs. From UV–VIS spectra a value of λ = 551 nm (2.25 eV) was calculated corresponding to the electronic transition of a single polyenyne chain. This energy is located at the low energy end of a yellow PDA solution spectrum. From Raman scattering v(CC) = 2108–2128 cm−1 and v(CC) = 1505–1532 cm−1 were calculated after extrapolation. Similarly sp-C13C NMR data yielded a shift of δ = 100 ppm. These data are…
Optical diagnostic of temperature in rocket engines by coherent Raman techniques
2004
Abstract This article reviews the study of Raman line shapes of molecular species involved in reactive media, such flames or engines, at high temperature and high pressure. This study is of interest from a fundamental as well as from a practical point of view with regards to the CARS temperature diagnostic of GH2–LOX combustion systems. We will particularly draw attention to recent investigations by means of Stimulated Raman Spectroscopy (SRS) in H2–H2O mixtures at temperature up to 1800 K. Whereas H2–X systems usually exhibit large inhomogeneous effects, due to the speed dependence of the collisional parameters, the absence of such apparent inhomogeneous signatures in the H2–H2O system all…
Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study
2015
The synthesis and characterization of the donor-acceptor substituted cyclometalated ruthenium(II) polypyridine complex isomers [Ru(dpb-NHCOMe)(tpy-COOEt)](PF6) 1(PF6) and [Ru(dpb-COOEt)(tpy-NHCOMe)](PF6) 2(PF6) (dpbH = 1,3-dipyridin-2-ylbenzene, tpy = 2,2';6,2"-terpyridine) with inverted functional group pattern are described. A combination of resonance Raman spectroscopic and computational techniques shows that all intense visible range absorption bands arise from mixed Ru → tpy/Ru → dpb metal-to-ligand charge transfer (MLCT) excitations. 2(PF6) is weakly phosphorescent at room temperature in fluid solution and strongly emissive at 77 K in solid butyronitrile matrix, which is typical for r…
Vibrational and rotational collisional relaxation in CO2–Ar and CO2–He mixtures studied by stimulated Raman-infrared double resonance
1999
0021-9606; The collisional relaxation among vibrational levels of the Fermi dyad of CO2 mixed with Ar and He (10% CO2, 90% rare gas) has been studied at room temperature with a double resonance experiment. Stimulated Raman effect from the ground state achieved the pumping process with a Nd:YAG laser and a pulse amplified dye laser. After pumping the v(1) or 2v(2)(Sigma(+)g) level, a cw CO2 laser was used to probe either the depopulation rates of the pumped levels (vibrationally or rotationally resolved) or the energy transfer rates to neighboring states. The vibrational energy relaxation has been studied from experimental depopulation of v(1) and population of 2v(2) levels through a five-le…
Phase behaviour of Ag2CrO4 under compression: Structural, vibrational, and optical properties
2013
We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of silver chromate (Ag2CrO4) at ambient temperature and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. When the initial orthorhombic Pnma Ag2CrO4 structure (phase I) is compressed up to 4.5 GPa, a previously undetected phase (phase II) has been observed with a 0.95% volume collapse. The structure of phase II can be indexed to a similar orthorhombic cell as phase I, and the transition can be considered to be an isostructural transition. This collapse is mainly due to the drastic contraction of the a ax…
Study of the benzene⋅N2 intermolecular potential-energy surface
2003
The intermolecular potential-energy surface pertaining to the interaction between benzene and N2 is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene–N2 van der Waals complex using the coupled cluster singles and doubles including connected triples [CCSD(T)] method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. After fitting the energies to an analytic function, the intermolecular Schrödinger equation is solved to yield energies, rotational constants, and Raman-scattering coefficients for the lowest intermolecular levels of several benzene–N2 isotopomers. Experimentally, intermolecula…
Computational and experimental investigation of intermolecular states and forces in the benzene-helium van der Waals complex
2003
A study of the intermolecular potential-energy surface (IPS) and the intermolecular states of the perprotonated and perdeuterated benzene–He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two- to four-body atom–atom terms is obtained. This IPS, and two other Lennard-Jones atom–atom surfaces from the literature, are each employed in dynamically exact (within the rigid-monomer approximation) calculations of J = 0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational trans…
Use of Spectroscopic Techniques to Monitor Changes in Food Quality during Application of Natural Preservatives: A Review
2020
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Aging of MCM41, MSU-H and MSU-F mesoporous systems investigated through the Raman spectroscopy
2014
Here we report an experimental investigation, based on the Raman spectroscopy, on the aging of some mesoporous silica based systems. In details, we studied the aging in air of the MCM41, the MSU-H and the MSU-F materials by acquiring the Raman spectra of as received and of mechanically pressed, at 0.2 and 0.45 GPa, powders. Our data evidenced that the starting powders of the MCM41 and of the MSU-H undergo structural modification when they are exposed to the ambient atmosphere, such modification consisting in the decrease of the D2 Raman band (originated by the three member rings). At variance the powders of the MSU-F appear to be stable. Furthermore, by pressing the starting powders to prod…