Search results for "Spectroscopy"
showing 10 items of 10293 documents
Competing factors on the frequency separation between the OH stretching modes in water
2015
Abstract Recent simulations demonstrated that the inhomogeneous broadening as observed in the vibrational spectra of liquid water at ambient conditions can be viewed as a large vibrational splitting of symmetric and asymmetric OH stretching modes, due to the asymmetry of the local hydrogen-bonding network [J. Phys. Chem. Lett., 2013, 4(19), pp 3245–3250]. In this work, we show that the finite temperature and the liquid phase do not only modulate the local hydrogen-bonding asymmetry of water molecules, but also the intramolecular coupling strength. These two factors compete together in the determination of the overall magnitude of the frequency separation between the two OH stretching modes …
Multi-Resolution error analysis of predicted absorption coefficients. Method and application to the infrared spectrum of methane at high temperature.
2010
La version V2 inclut les modifications proposées par les reviewers.; International audience; A general method for the estimation of the confidence interval of molecular absorption coefficients is presented. Statistical numerical experiments are implemented to quantify the propagation of errors from line parameters to absorption coefficients or cross-sections as a function of the resolution. The method uses line parameter predictions (position and intensity) with estimated uncertainties derived from global polyad models. This work is especially intended to provide expert information for applications requiring theoretical predictions for which the present state of the art of line by line high…
Soret coefficient of trace ions determined with electrochemical impedance spectroscopy in a thin cell. Theory and measurement
2018
The tendency of a substance to migrate due to a temperature gradient is known as thermodiffusion or the Soret effect. We believe that this is the first work that describes the study of the Soret effect using electrochemical impedance spectroscopy in a non-isothermal thin cell, and shows how the Soret coefficient can be determined from these measurements. The effect of a temperature gradient in a thin cell is analyzed, both theoretically and experimentally. Our theoretical modeling of the system predicts the effect of key parameters to the impedance spectra. Experimentally we determine the Soret coefficient of the redox couple Fe(CN)64−/Fe(CN)63− in an aqueous KCl solution. It is found that …
Some observations on the prediction of retention in reversed-phase liquid chromatography using the pH as main factor
2004
Abstract When solutes show acid–base behaviour inside the working pH of a reversed-phase liquid chromatographic (RPLC) column, besides the type and percentage of organic modifier, pH can be included to improve the possibilities of separation. Optimisation based on a retention model is an economical and reliable way to achieve the best resolution. However, the difficulties found in knowing the exact pH values and the dependence of acid−base constants of solutes with mobile phase composition makes the accurate modelling of the retention behaviour as a function of these variables rather difficult. In this work, it is shown that in fact, there is no need to have this information. Based on the e…
Membrane Deformation and Its Effects on Flow and Mass Transfer in the Electromembrane Processes
2019
In the membrane processes, a trans-membrane pressure (TMP) may arise due to design features or operating conditions. In most applications, stacks for electrodialysis (ED) or reverse electrodialysis (RED) operate at low TMP (<
Analytic evaluation of Raman intensities in coupled-cluster theory
2007
We present the first implementation for the analytic calculation of polarizability derivatives using coupled-cluster theory. These derivatives are related to the intensity of bands seen in Raman spectroscopy, and are therefore important quantities that can also be measured experimentally. The required theory of analytic third derivatives is discussed and also connected to response theory to allow the calculation of frequency-dependent quantities. This work includes the use of a string-based general coupled-cluster/configuration-interaction program which makes the calculation of Raman intensities for arbitrary coupled-cluster or configuration-interaction methods up to the full configuration-…
Thermodynamics and Kinetics of Adsorption of Gaseous Single Cl/Br-VOCs of the Ethane Series onto Siliceous ZSM-5 at 25 °C. Prediction of the Adsorpti…
2001
This work deals with a thermodynamic and kinetic experimental study of adsorption of gaseous single Cl/Br-VOCs (1,2-dichloroethane, 1-bromo-2-chloroethane, and 1,2-dibromoethane) onto siliceous ZSM-5 at 25 °C. The adsorbed amounts, adsorption heats, and diffusivities were simultaneously obtained. The isotherms were of the type I and verified Henry's law in a very large domain of filling. The adsorption heats and the diffusivities of the brominated molecules displayed specific behaviors probably owing to a transport resistance. The comparison of the relative position of isotherms and the adsorption heats allowed us to predict that the competitive adsorption of their mixture would be similar …
High energy, high resolution photoelectron spectroscopy of Co2Mn(1-x)Fe(x)Si
2006
This work reports on high resolution photoelectron spectroscopy for the valence band of Co2Mn(1-x)Fe(x)Si (x=0,0.5,1) excited by photons of about 8 keV energy. The measurements show a good agreement to calculations of the electronic structure using the LDA+U scheme. It is shown that the high energy spectra reveal the bulk electronic structure better compared to low energy XPS spectra. The high resolution measurements of the valence band close to the Fermi energy indicate the existence of the gap in the minority states for all three alloys.
Efficient Hot Electron Transfer in Quantum Dot-Sensitized Mesoporous Oxides at Room Temperature
2018
Hot carrier cooling processes represent one of the major efficiency losses in solar energy conversion. Losses associated with cooling can in principle be circumvented if hot carrier extraction toward selective contacts is faster than hot carrier cooling in the absorber (in so-called hot carrier solar cells). Previous work has demonstrated the possibility of hot electron extraction in quantum dot (QD)-sensitized systems, in particular, at low temperatures. Here we demonstrate a room-temperature hot electron transfer (HET) with up to unity quantum efficiency in strongly coupled PbS quantum dot-sensitized mesoporous SnO2. We show that the HET efficiency is determined by a kinetic competition b…
Up-Conversion Luminescence Processes in NaLaF4 Doped with Tm3+ and Yb3+ and Dependence on Tm3+ Concentration and Temperature
2021
In this work, luminescence processes in polycrystalline NaLaF4:Tm3+ and NaLaF4:Tm3+,Yb3+ materials were studied. Luminescence spectra and decay kinetics measurements were performed for NaLaF4 doped with various Tm3+ concentrations (0.01, 0.1, 0.5, 1, and 2 mol%) under direct excitation to 3P0, 1D2, 1G4, and 3H4 states. It was found that some of the Tm3+ excited states are more affected by Tm3+ concentration than other states. Under infrared excitation of Yb3+, energy transfer to Tm3+ occurred and intensive ultraviolet and blue up-conversion luminescence was observed. Possible up-conversion mechanisms are discussed. Spectroscopic measurements show that long-duration excitation radiation red…