Integral equation theory description of phase equilibria in classical fluids

Infrared Spectroscopy Mirosław Antoni Czarnecki,*,† Yusuke Morisawa,‡ Yoshisuke Futami, and Yukihiro Ozaki* †Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland ‡Department of Chemistry, School of Science and Engineering, Kinki University, Higashi-Osaka, Osaka 577-8502, Japan Department of Biological and Chemical Systems Engineering, National Institute of Technology, Kumamoto College, Yatsushiro, Kumamoto 866-8501, Japan Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan

Advances in Molecular Structure and Interaction Studies Using Near-Infrared Spectroscopy.

Atmospheric field measurements and models of the stratospheric sulfate aerosol layer led to the suggestion that sulfuric acid (H2SO4) must photolyze at high altitudes. We propose that excitation of vibrational overtones of H2SO4 and its hydrate in the near-infrared and visible leads to photolysis, forming sulfur trioxide (SO3) and water. On the basis of absorption cross sections calculated with ab initio methods calibrated to experimental measurements, we estimated J values that are sufficient to explain stratospheric and mesospheric sulfur dioxide (SO2) concentrations and the observation of the sulfate layer.

Photolysis of Sulfuric Acid Vapor by Visible Solar Radiation

We have calculated fundamental and overtone OH-stretching vibrational band intensities of the water dimer and trimer. The intensities were determined with a simple harmonically coupled anharmonic oscillator (HCAO) local mode model and ab initio dipole moment functions. The dipole moment functions were calculated at the self-consistent-field Hartree–Fock and quadratic configuration interaction including single and double excitations levels of theory with the 6–31G(d), 6–311+G(d,p), and 6–311++G(2d,2p) basis sets. The overtone spectra of the dimer and trimer have not been observed and a method of obtaining local mode parameters from scaled ab initio calculations has been suggested. We find that the falloff in absolute intensity with increasing overtone of the dimer and trimer is similar to the falloff observed for the monomer. Our calculations show that the total overtone intensity of the dimer and trimer, although distributed differently, is close to two and three times the total intensity of the monomer f...

Calculation of OH-stretching band intensities of the water dimer and trimer

Intermolecular interactions in molecular clusters can significantly alter the optical properties and reaction dynamics of the constituent monomers. As a result, both atmospheric chemistry and climate may be affected. We review here the spectroscopy and photochemistry of molecular hydrates and point to their possible relevance to the Earth's atmosphere. Data needed to model the atmospheric effects of hydrates includes calculation of both their abundance and their absorption cross-section. We discuss these issues and examine the potential spectroscopic effects of hydrates in the atmosphere, as well as the fundamental work needed to quantify better the magnitude of these effects.

Hydrated Complexes: Relevance to Atmospheric Chemistry and Climate

The gas phase vibrational overtone spectrum of propane is measured using conventional near infrared (NIR) spectroscopy for the ΔvCH=2–5 regions and intracavity dye laser photoacoustic spectroscopy (IDL‐PAS) for the ΔvCH=5 and 6 regions. The peaks are assigned in terms of the local mode model. Experimental oscillator strengths are compared to values calculated for the CH‐stretching components of the spectrum. The calculations use a harmonically coupled, anharmonic oscillator local mode model to obtain the vibrational wave functions, and ab initio MO calculations at the SCF level with a 6‐31G* basis set to obtain the dipole moment function. The importance of intermanifold coupling is explored. The calculations can account for the fall‐off in intensity with increasing v, and can give a reasonably quantitative account of the relative intensities of the individual peaks within a given vibrational manifold. The questions of the relative intensities of primary and secondary CH bonds, and of the relative intensities of different methyl CH bonds are also explored.

Intensities in local mode overtone spectra: Propane

Dependence of an Acoustically Nonresonant Intracavity Photoacoustic Signal on Sample and Buffer Gas Pressure

Trimethylcyclohexane: overtone spectrum, ab initio calculations, and unusual chemical shifts

The CH stretching overtone spectra of 1,3- and 1,4-cyclohexadiene have been recorded in the regions corresponding to Δv = 2−6. Bands are assigned as overtones of the various nonequivalent CH bonds. Oscillator strengths have been calculated according to the harmonically coupled anharmonic oscillator (HCAO) local mode (LM) model, with ab initio dipole moment functions. The theoretical values have been compared to experimental values, and good agreement is found between predicted intensities and measured relative intensities within an overtone band. For 1,4-cyclohexadiene, shoulders were observed approximately 100 cm-1 above and below the pure LM transition for Δv ≥ 4. These are assigned as (±) combinations with a low-frequency ring-puckering mode.

Bernhard J. Schattka

Papers

Intensities in local mode overtone spectra: Propane

Dependence of an Acoustically Nonresonant Intracavity Photoacoustic Signal on Sample and Buffer Gas Pressure

Trimethylcyclohexane: overtone spectrum, ab initio calculations, and unusual chemical shifts

Relative intensities of nonequivalent ch bonds in the local mode overtone spectra of 1,3-and 1,4-cyclohexadiene

Trimethylcyclohexane: Overtone Spectrum, ab initio Calculations, and Unusual Chemical Shifts