High-resolution molecular fingerprinting in the 11.6-15 μm range by a quasi-CW difference-frequency-generation laser source

We report an approach for high-resolution spectroscopy using a widely tunable laser emitting in the molecular fingerprint region. The laser is based on difference-frequency generation (DFG) in a nonlinear orientation-patterned GaAs crystal. The signal laser, a CO2 gas laser, is operated in a kHz-pulsed mode while the pump laser, an external-cavity quantum cascade laser, is finely mode-hop-free tuned. The idler radiation covers a spectral range of ∼11.6-15 μm with a laser linewidth of ∼ 2.3 MHz. We showcase the versatility and the potential for molecular fingerprinting of the developed DFG laser source by resolving the absorption features of a mixture of several species in the long-wavelength mid-infrared. Furthermore, exploiting the wide tunability and resolution of the spectrometer, we resolve the broadband absorption spectrum of ethylene (C2H4) over ∼13-14.2 μm and quantify the self-broadening coefficients of some selected spectral lines

Chemical auxiliaries free dyeing of cationized cotton with 1:2 metal complex dye

Application of 1:2 metal complex dyes on pre-cationized cotton has been studied. This unconventional process avoids the use of electrolyte required as exhausting agent in conventional dyeing of cotton fabric. Indeed, when we use a large amount of salt, the discharged wastewater from dye house creates unavoidable environmental threats. The dyeing has been carried out at the liquor ratio of 1:40 in a sealed stainless steel dyebath housed on the Ahiba Nuance speed varying temperature, contact time and sulphate concentration. Optimal conditions are determined using the experimental designs method. The results show the possibility of chemical auxiliaries free dyeing of cotton fabrics with 1:2 metal complex dye at 75°C for 15 min by treating them with cationizer prior to dyeing. Adsorption kinetic and isotherm are also studied and the parallel exponential model is shown to fit experimental data with higher average regression coefficients

Importance du phénomène de dissolution-cristallisation sur le fluage d'une craie blanche Importance of the Dissolution-Crystallization Phenomenon on Creep in a White Chalk

Une étude de fluage de craie blanche a été menée pour des contraintes de confinement allant jusqu'à 12 MPa dans des configurations de contrainte isotrope ou avec léger déviateur. Il est montré l'importance du phénomène de dissolution sur la variation de volume locale du système. Celle-ci suit une loi du type At alpha avec alpha de l'ordre de 0,5 lorsqu'il n'y a pas d'écoulement, et de l'ordre de 0,65 quand l'échantillon est soumis à un écoulement. Il est alors proposé le modèle de Bathurst comme mécanisme de déformation. Creep in a white chalk was analyzed for confining pressures of up to 12 MPa in isotropic stress configurations or with a slight deviatoric stress. The importance of this dissolution phenomenon was shown for the local variation in the volume of the system. This variation follows a law of the At alpha type, with alpha being a 0. 5 order when there is no flow and a 0. 65 order when the sample is subjected to flow. The Bathurst model is then proposed as the deformation mechanism

Importance du phénomène de dissolution-cristallisation sur le fluage d'une craie blanche

Une étude de fluage de craie blanche a été menée pour des contraintes de confinement allant jusqu'à 12 MPa dans des configurations de contrainte isotrope ou avec léger déviateur. Il est montré l'importance du phénomène de dissolution sur la variation de volume locale du système. Celle-ci suit une loi du type At alpha avec alpha de l'ordre de 0,5 lorsqu'il n'y a pas d'écoulement, et de l'ordre de 0,65 quand l'échantillon est soumis à un écoulement. Il est alors proposé le modèle de Bathurst comme mécanisme de déformation

A mid-infrared diagnostic for benzene using a tunable difference-frequency-generation laser

Benzene is a very important molecule in a variety of industrial, environmental, and chemical systems. In combustion, benzene plays an essential role in the formation and growth of polycyclic aromatic hydrocarbons and soot. In this work, a new laser-based diagnostic is presented to make quantitative, interference-free, and sensitive measurements of benzene in the mid-infrared (MIR) region. The diagnostic is based on a widely tunable difference-frequency-generation (DFG) laser system. We developed this laser source to emit in the MIR between 666.54 cm-1 and 790.76 cm-1 as a result of the DFG process between an external-cavity quantum-cascade-laser and a CO2 gas laser in a nonlinear, orientation-patterned GaAs crystal. Benzene measurements were carried out at the peak (673.94 cm-1) of the Q-branch of the v11 vibrational band of benzene. The absorption cross-section of benzene was measured over a range of pressures (4.44 mbar to 1.158 bar) at room temperature. The temperature dependence of the absorption cross-section was studied behind reflected shock waves over 553-1473 K. The diagnostic was demonstrated in a high-temperature reactive experiment of benzene formation from propargyl radicals. The new diagnostic will prove highly beneficial for high-temperature studies of benzene formation and consumption kinetics

Experimental and kinetic modeling study of tetralin: A naphtheno-aromatic fuel for gasoline, jet and diesel surrogates

Distillate fuels contain significant proportions of naphtheno-aromatic components and tetralin is a suitable surrogate component to represent this molecular moiety. The presence of aromatic and naphthyl rings makes kinetic modeling of tetralin very challenging. Primary radicals formed during the oxidation of tetralin can be aryl, benzylic or paraffinic in nature. Using available information on reaction paths and rate constants of naphthenes and alkyl-aromatics, a kinetic model of tetralin has been developed in the current study with emphasis on low-temperature chemistry and high-pressure conditions. Due to the lack of high-level quantum chemical calculations on reaction pathways of tetralin, analogous rates from ab-initio studies on benzylic and paraffinic radicals have been adopted here. Some modifications to the reaction rate rules are incorporated to account for the unique characteristics of tetralin's molecular structure. Important reaction channels have been identified using reaction path and brute force sensitivity analyses. In order to investigate the model performance at low temperatures, new experiments are carried out in a rapid compression machine on blends of tetralin and 3-methylpentane. Blending of low-reactivity tetralin with a high-reactivity alkane allowed the investigation of tetralin ignition at very low temperatures (665 – 856 K). The kinetic model developed in the current study is found to predict the current experiments and literature data adequately. The new model will aid in high-fidelity surrogate predictions at engine-relevant conditions