Water Absorption Spectroscopy Research Articles

Electronic and thermodynamic study of Indium (III) complex with N-ethyl-sulfonyldithiocarbimate

Dithiocarbimate complexes are commonly utilized in research as vulcanization accelerators in the curing of rubber. This work describes the synthesis and thermodynamic study of an Indium (III) complex containing N-ethyl-sulfonyldithiocarbimate as ligand. The ligand degradation was investigated in water via electronic absorption spectroscopy in water. In addition, X-ray diffraction allowed us to identify the structure of the degradation product. The electronic absorption spectroscopy was also used to identify the absorption band related to the coordination process. Formation of the complex was analysed by isothermal titration calorimetry, which not only suggested a 1:2 metal to ligand stoichiometry, but also identified the thermodynamic parameters for the coordination process. These data demonstrated a favourable enthalpic variation (ΔHo < 0) for both sites and a positive entropic variation (TΔSo > 0) for the second site, corroborating the geometry change during the titration process. This was further investigated by DFT calculations regarding the structure and stability of ligand and complex formation complementing the overall conclusions of the experimental data by geometry, electronic transitions and vibrational analysis of the system.

Force-detected nanoscale absorption spectroscopy in water at room temperature using an optical trap.

Measuring absorption spectra of single molecules presents a fundamental challenge for standard transmission-based instruments because of the inherently low signal relative to the large background of the excitation source. Here we demonstrate a new approach for performing absorption spectroscopy in solution using a force measurement to read out optical excitation at the nanoscale. The photoinduced force between model chromophores and an optically trapped gold nanoshell has been measured in water at room temperature. This photoinduced force is characterized as a function of wavelength to yield the force spectrum, which is shown to be correlated to the absorption spectrum for four model systems. The instrument constructed for these measurements combines an optical tweezer with frequency domain absorption spectroscopy over the 400-800 nm range. These measurements provide proof-of-principle experiments for force-detected nanoscale spectroscopies that operate under ambient chemical conditions.

Electron Transfer Reaction Dynamics of p-Nitroaniline in Water from Liquid to Supercritical Conditions

Photoexcitation dynamics of p-nitroaniline (pNA) have been investigated by femto-second transient absorption spectroscopy in water from liquid to supercritical conditions; along the isochoric line from the ambient condition to 664 K at 40.1 MPa and along the isothermal line from 40.1 to 36.1 MPa at 664 K. The rates of the back electron transfer reaction from the photoexcited charge transfer state to the electronic ground state was determined by the bleach recovery of the ground state absorption, and the successive vibrational relaxation in the electronic ground state was determined by the hot-band decay which was apparent at the red edge of the absorption. The variation of the back electron transfer rate was compared with the prediction based on the electron transfer theory including the Franck-Condon active vibrational modes. The results indicated that both the free energy change of the reaction and the change of the intramolecular vibrational reorganization energy cause the characteristic density (or temperature) dependence of the back electron transfer rate. The density dependence of the vibrational relaxation rate was compared with the collision frequency and the coordination number of the solvent molecule around the solute estimated by the molecular dynamics simulations. The density dependence of the coordination of a water oxygen atom to an amino hydrogen atom of pNA was found to be correlated with the density dependence of vibrational relaxation rate.

An experimental investigation of gas-phase combustion synthesis of SiO 2 nanoparticles using a multi-element diffusion flame burner

The current work presents the results of an experimental investigation of gas-phase combustion synthesis of silica (SiO 2) particles using a multi-element diffusion flame burner (MEDB, a Hencken burner). Silane (SiH 4) was added to hydrogen/oxygen/argon (H 2/O 2/Ar) flames to produce SiO 2 nanoparticles at various burner operating conditions (φ = 0.47–2.16). To characterize the burner performance, temperature measurements were made using water absorption spectroscopy and uncoated, fine-wire thermocouples. The results demonstrated the non-premixed flow arrangement of the fuel tubes and oxidizer channels of the MEDB provided uniform, ∼1D conditions above the surface of the burner, with temperature variations of less than ±3% in the transverse direction (parallel to the surface of the burner) for elevations above the mixing region (z = 0–7 mm), extending to heights ≥ 30 mm. At heights above the mixing region, approximately constant axial temperatures are also observed. Silica particle formation and growth were examined for comparison with current understanding of the physical mechanisms important in combustion synthesis of SiO 2. The particle properties were determined using transmission electron microscope (TEM) imaging. Geometric mean diameters of the primary particles varied from d̄ p = 9 to 18 nm. The current study demonstrates the utility of the MEDB in providing a controlled environment for fundamental studies of gas-phase combustion synthesis phenomena, as well as offering broad flexibility in experimental design with control over process variables such as temperature field, particle residence time, scalable reactant loading, and particle precursor selection.

H2O absorption spectroscopy for determination of temperature and H2O mole fraction in high-temperature particle synthesis systems.

Water absorption spectroscopy has been successfully demonstrated as a sensitive and accurate means for in situ determination of temperature and H2O mole fraction in silica (SiO2) particle-forming flames. Frequency modulation of near-infrared emission from a semiconductor diode laser was used to obtain multiple line-shape profiles of H2O rovibrational (v1 + v3) transitions in the 7170-7185-cm(-1) region. Temperature was determined by the relative peak height ratios, and XH2O was determined by use of the line-shape profiles. Measurements were made in the multiphase regions of silane/hydrogen/oxygen/ argon flames to verify the applicability of the diagnostic approach to combustion synthesis systems with high particle loadings. A range of equivalence ratios was studied (phi = 0.47 - 2.15). The results were compared with flames where no silane was present and with adiabatic equilibrium calculations. The spectroscopic results for temperature were in good agreement with thermocouple measurements, and the qualitative trends as a function of the equivalence ratio were in good agreement with the equilibrium predictions. The determinations for water mole fraction were in good agreement with theoretical predictions but were sensitive to the spectroscopic model parameters used to describe collisional broadening. Water absorption spectroscopy has substantial potential as a valuable and practical technology for both research and production combustion synthesis facilities.