Multispectrum analysis of the ν9 band of C2H6: Positions, intensities, self- and N2-broadened half-width coefficients

Line positions, intensities, Lorentz self- and N₂-broadened half-width coefficients have been measured for ^PQ₃, ^PQ₂, ^PQ₁, ^RQ₀, ^RQ₁, ^RQ₂, and ^RQ₃ sub-band transitions in the ν₉ fundamental band of ¹²C₂H₆. A multispectrum nonlinear least-squares fitting technique was used to fit up to 17 high-resolution (∼0.00156 cm⁻¹), room temperature absorption spectra of pure (99.99% chemical purity) natural sample of ethane and lean mixtures of the high-purity ethane diluted with N₂. A Bruker IFS 120HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington was used to record the data. A standard Voigt line shape was assumed to fit all the data since no line mixing or other non Voigt line shapes were required to fit any of the spectra used in the analysis. Short spectral intervals (∼2-2.5 cm⁻¹) of all 17 spectra covering a specific ^PQ or ^RQ sub-band were fit simultaneously. For the first time in an ethane band, pressure-broadened half-width coefficients were determined for the torsional-split components. However, for better reliability of the retrieved coefficients for the weaker components (transitions with large intensity ratios of 4:1 or 3:1 for most K levels between the strong and weak components), constraints were used such that the half-width coefficients of both torsional-split components for a given J were identical for a specific broadening gas. No pressure-induced shift coefficients were necessary to fit the spectra to their noise level. The present study revealed for the first time the dependence of self- and N₂-broadened half-width coefficients upon the J, K quantum numbers of the transitions in ethane. A number of transitions belonging to the ν₉+ν₄−ν₄ and the ν₉+2ν₄−2ν₄ hot bands were also observed in the fitted regions and measurements were made when possible.     

High-power, continuous-wave Ti:sapphire laser pumped by fiber-laser green source at 532 nm

We report the first experimental demonstration of efficient and high-power operation of a Ti:sapphire laser pumped by a simple, compact, continuous-wave (cw) fiber-laser-based green source. The pump radiation is obtained by direct single-pass second-harmonic-generation (SHG) of a 33 W, cw Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal, providing 11 W of single-frequency green power at 532 nm in TEM₀₀ spatial profile with power and frequency stability better than 3.3% and 32 MHz, respectively, over 1 h. The Ti:sapphire laser is continuously tunable across 743-970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM₀₀ spatial profile with M²<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 h.     

Dehydration of 1,4-dioxane through blend membranes of poly(vinyl alcohol) and chitosan by pervaporation

Blend membranes prepared from poly(vinyl alcohol) (PVA) and chitosan (CS) were crosslinked with glutaraldehyde and used in the pervaporation dehydration of 1,4-dioxane. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (X-RD) to assess, respectively, the intermolecular interactions, thermal stability and crystallinity. Equilibrium sorption studies were carried out in pure liquids and binary mixtures of different compositions of water + 1,4-dioxane mixtures to assess the polymer–liquid interactions. The crosslinked membrane showed a good potential in breaking the azeotrope of 82 wt.% aqueous 1,4-dioxane giving a selectivity of 117 with a reasonable water flux of 0.37 kg/m² h. The effect of operating parameters such as feed composition, membrane thickness and permeate pressure was evaluated.     

Sonochemical synthesis and properties of nanoparticles of FeSbO4

A sonochemical method was employed to prepare reactive nanoparticles of FeSbO(4) at 300 °C, which is the lowest calcination temperature reported so far for preparing FeSbO(4). A systematic evolution of the FeSbO(4) phase formation as a function of temperature was monitored by in situ synchrotron X-ray measurements. The 300 and 450 °C calcined powders exhibited specific surface areas of 116 and 75 m(2)/g, respectively. The X-ray photoelectron spectra analysis confirmed the presence of mainly Fe(3+) and Sb(5+) in the calcined powder. The response of the fabricated sensors (using both 300 and 450 °C calcined powders) toward 1000 ppm and 1, 2, 4, and 8% hydrogen, respectively, has been monitored at various operating temperatures. The sensors fabricated using 300 °C calcined powder exhibited a response of 76% toward 4% H(2) gas at an operating temperature of 300 °C, while those fabricated using 450 °C calcined powder exhibited a higher response of 91% with a quick recovery toward 4% H(2) gas at 300 °C. The results confirmed that a higher calcination temperature was preferred to achieve better sensitivity and selectivity toward hydrogen in comparison to other reducing gases such as butane and methane. The experimental results confirmed that the sonochemical process can be easily used to prepare FeSbO(4) nanoparticles for various catalytic applications as demonstrated. Here, we project FeSbO(4) as a new class of material exhibiting high sensitivity toward a wide range of hydrogen gas. Such sensors that could detect high concentrations of hydrogen may find application in nuclear reactors where there will be a leakage of hydrogen.     

Synthesis of oxalate doped polyaniline and its corrosion protection performance

It is known that dopants present in polyaniline (PANI) play an important role in corrosion protection of mild steel since the dopant ions form a secondary layer with iron. Since oxalate ions form a stable iron oxalate layer on mild steel, a study has been made on the corrosion protection performance of steel by vinyl coating containing oxalate doped PANI in acid and neutral media. Electrochemical impedance spectroscopy (EIS) studies have shown that the oxalate doped PANI is able to protect mild steel in sodium chloride solution since the impedance values are maintained at 10¹⁰ Ω cm² even after 100 days of exposure.     

First stereoselective total synthesis of triumfettamide

The first total synthesis of triumfettamide (1) is described. The asymmetric syntheses of two highly functionalized units—α-hydroxylated C17 monounsaturated fatty acid unit (2) and C26 phytosphingosine (3) have been accomplished involving Sharpless asymmetric dihydroxylation, Sharpless kinetic resolution, regioselective epoxide opening, regioselective DIBAL-H reduction of acetal, Wittig olefination as the key steps. Finally N-acylation of phytosphingosine 3 with (2R,6Z)-2-hydroxy-6-heptadecenoic acid 2 followed by DDQ deprotection of PMB, provided target compound 1.     

New catanionic surfactants, phase stability and synthesis of ultrafine CdS nanoparticles

A systematic study on the water-intake capacity of the microemulsion formed using a catanionic surfactant (synthesized by taking equimolar mixture of acid and amine) with varying hydrocarbon chain length of the acid has been carried out. A decrease in the water-intake capacity with increase in the chain length was observed. Shorter chain length of co-surfactant (1-butanol compared to 1-octanol) led to higher water-intake capacity of microemulsions which may also be attributed to the high hydrophilic-lipophilic balance (HLB) of 1-butanol. Three new microemulsions based on catanionic surfactants have been used to synthesize quantum dots of CdS. The size of CdS quantum dots decreased with increase in chain length of the acid component of the catanionic surfactant.     

Visible Light‐Induced,Metal‐Free Denitrative [3+2] Cycloaddition for Trisubstituted Pyrrole Synthesis

A metal‐free, regioselective synthesis of trisubstituted pyrroles has been developed through a formal [3+2] cycloaddition reaction between 2H‐azirines and nitroalkenes under visible light/photoredox‐catalyzed conditions. The reaction proceeds through 2H‐azaallenyl radical addition on β‐nitrostyrenes in a Michael fashion followed by a base‐mediated denitration reaction. The directive group influence of the nitro group controls the regiochemistry of the reaction.     

Indirect electrochemical oxidation of substituted polycyclic aromatic hydrocarbons to corresponding para-quinones with potassium bromide in water–chloroform medium

Indirect electrochemical synthesis of quinone derivatives of a series of substituted anthracene and naphthalene by the electrolysis of aqueous solution of potassium bromide (3.0 M) using Pt anode at constant current density (40 mA/cm²) has been carried out. These reactions resulted in good to excellent yields of the corresponding para-quinones as confirmed by physical and spectral data.     

Viscosity-Temperature Behavior of Hydroxypropyl Cellulose Solution in Presence of an Electrolyte or a Surfactant: A Convenient Method to Determine the Cloud Point of Polymer Solutions

The viscosity of hydroxypropyl cellulose (HPC) solution with or without an additive has been measured continuously as a function of temperature with the help of a vibro-viscometer. The viscosity of the polymer solution showed a gradual decrease initially with increase in temperature until a particular point beyond which there was a sharp decrease in the viscosity, which coincided with the clouding of the solution. The cloud point temperature (CP) of the polymer solution was determined from the first derivative plot of viscosity vs. temperature. Effect of addition of an electrolyte or a surfactant on the CP of HPC solution has also been studied. While a decrease in CP of HPC solution in presence of fluoride, chloride, or bromide ions was observed, presence of iodide or thiocyanide ions led to an increase in the CP. However, presence of an ionic surfactant initially lowered the CP but beyond a particular surfactant concentration a sharp increase in cloud point was observed due to interaction of the surfactant with the polymer. The results suggest that surfactants with longer hydrophobic tail or more hydrophobic groups have more affinity for HPC.