Photoacoustic Detection of Weak Absorption Bands in Infrared Spectra of Calcite

Photoacoustic spectroscopic detection of infrared absorption often produces spectra with enhanced intensities for weaker peaks, enabling the detection of features due to overtones and combinations, as well as less-abundant isotopic species. To illustrate this phenomenon, we present and discuss photoacoustic infrared spectra of calcite. We use linearization of rapidscan spectra, as well as comparing step-scan and rapid-scan spectra, to demonstrate that saturation is not the driving force behind these enhanced intensities. Our results point to a significant knowledge gap, since a theoretical basis for the enhancement of these weak bands has not yet been developed

Photoacoustic IR spectroscopy: instrumentation, applications and data analysis

This invaluable and up-to-date source on instruments and applications covers everything needed to employ a technique for investigating various gases and materials, including biomaterials. It includes the latest developments in light sources, signal recovery and numerical methods. There is no other single publication that reviews the entire subject of photoacoustic infrared spectroscopy in such detail. Physicists, chemists, and spectroscopists in both academic and industrial laboratories, polymer and organic chemists, analysts in industry, forensic and government laboratories, and materials scientists will find this book to be a vital resource

Characterization of OCS-HCCCCH and N2O-HCCCCH Dimers: Theory and Experiment

The infrared spectra of the weakly-bound dimers OCS-HCCCCH, in the region of the v1fundamental band of OCS (2050 cm-1), and N2O-HCCCCH, in the region of the v1fundamental band of N2O (2200 cm-1), were observed in a pulsed supersonic slit jet expansion probed with tunable diode/QCL lasers. Both OCS-HCCCCH and N2O-HCCCCH were found to have planar structure with side-by-side monomer units having nearly parallel axes. These bands have hybrid rotational structure which allows for estimates of the orientation of OCS and N2O in the plane of their respective dimers. Analogous bands for OCS-DCCCCD and N2O-DCCCCD were also observed and found to be consistent with the normal isotopologues. Various levels of ab initio calculations were performed to find stationary points on the potential energy surface, optimized structures and interaction energies. Four stable geometries were found for OCS-HCCCCH and three for N2O-HCCCCH. The rotational parameters at CCSD(T∗)-F12c level of theory give results in very good agreement with those obtained from the observed spectra. In both dimers, the experimental structure corresponds to the lowest energy isomer

Micro-solvation of CO in water: Infrared spectra and structural calculations for (D2O)2 - CO and (D2O)3 - CO

The weakly-bound molecular clusters (D2O)2-CO and (D2O)3-CO are observed in the C-O stretch fundamental region (~2150 cm-1), and their rotationally-resolved infrared spectra yield precise rotational parameters. The corresponding H2O clusters are also observed, but their bands are broadened by predissociation, preventing detailed analysis. The rotational parameters are insufficient in themselves to determine cluster structures, so ab initio calculations are employed, and good agreement between experiment and theory is found for the most stable cluster isomers, yielding the basic cluster geometries as well as confirming the assignments to (D2O)2-CO and (D2O)3-CO. The trimer, (D2O)2-CO, has a near-planar geometry with one D atom from each D2O slightly out of the plane. The tetramer, (D2O)3-CO, has the water molecules arranged in a cyclic quasi-planar ring similar to the water trimer, with the carbon monoxide located ‘above’ the ring and roughly parallel to its plane. The tunneling effects observed in the free water dimer and trimer are quenched by the presence of CO. The previously observed water-CO dimer together with the trimer and tetramer reported here represent the first three steps in the solvation of carbon monoxide

Temperature coefficients of the refractive index for hydrocarbons and binary mixtures

Temperature coefficients of the refractive index (dn/dT) for nine hydrocarbons and two sets of binary mixtures were investigated in this work. The measured 12dn/dT values for the pure hydrocarbons were found to be inversely proportional to their molar volumes (Vm) and molecular weights (M). Experimental data for binary mixtures show that 12dn/dT varies linearly with volume and mass fractions, consistent with theory derived from the linear relationships of 12dn/dT with 1/Vm and 1/M for individual hydrocarbons. This study should aid the interpretation of the observed correlations of dn/dT with physical and combustion properties of diesel fuels.Peer reviewed: YesNRC publication: Ye

Correlations among thermophysical properties, ignition quality, volatility, chemical composition, and kinematic viscosity of petroleum distillates

Thermophysical measurements and Raman spectroscopy were utilized to investigate 17 hydrocarbon distillates derived from Canadian oil sands in this work. Thermal lens and optical interferometer techniques were used to determine the thermal diffusivity (D) and temperature coefficient of the refractive index (dn/dT), respectively. It was found that D and dn/dT are closely correlated with the cetane numbers, distillation temperatures, monocyclic aromatics contents, and kinematic viscosities of the fuels. Raman spectra yielded information on the chemical compositions of the distillates, with aromatic contents proving to be particularly relevant. Multivariate analysis elucidated the relationships among the samples, their properties according to ASTM analyses, and the influence of composition on D and dn/dT.Peer reviewed: YesNRC publication: Ye

Vibrational Spectroscopy and Thermophysical Properties of Ultralow Sulfur DieselAlternative Fuel Binary Blends

Four alternative fuels (AF) were blended with ultralow sulfur diesel (ULSD) at five different proportions (10, 20, 30, 50, and 100 vol % AF) to create 20 binary mixtures in this work. Two renewable jet AFs and two renewable diesel AFs were investigated. Interactions between the components in the mixtures were analyzed by means of spectroscopy (Raman, near-infrared), thermophysical (thermal diffusivity, thermo-optic coefficient), and physical (density) techniques. Correlations among the data were investigated using principal component analysis and partial least-squares regression. Trends in Raman intensities and band positions as well as thermophysical properties showed that the AF/ULSD blends resembled two-component mixtures despite the known complexities of the constituents. Specifically, spectra combined according to the percentages of the components in each mixture; thermophysical and physical properties exhibited similar behavior. The spectra showed strong correlations with all three physical properties, creating the possibility for predicting the properties of similar AF/ULSD mixtures. These properties are governed by the chemical compositions of the fuels