George Turrell

Spectroscopic studies of liquid alkanes using DCl as a molecular probe

Abstract The infrared spectra of DCl dissolved in a large number of branched and normal liquid alkanes have been related to structural properties of these solvents. Both the free volume and the shape of the alkane molecule have direct effects on the form of the vibration-rotation fundamental of the DCl solute. The results are analyzed using a correlation function approach and some calculations of molecular torque are reported.

Vibration—rotation spectra of CO in liquid alkanes

Vibration—rotation infrared spectra have been obtained for CO dissolved in a variety of branched and normal alkanes. The normalized band profiles yield rotational correlation functions, correlation times and the torques acting on the CO molecule. These quantities and the band shape depend only on the alkane free volume, contrasting with the situation for DC1 solute where they showed a strong dependence on solvent molecular shape. The Gordon m-diffusion model for rotational diffusion gives good predictions for the correlation functions and a complete fit is obtained using the generalized m-diffusion model incorporating a small frequency-dependence of the effectiveness of a collision in changing the rotor angular momentum. This success of simple stochastic theory contrasts with its failure for DCl in these alkanes.

Anharmonicity of the OH stretching vibration of acetic acid in nonpolar and slightly polar solvents

Abstract Frequencies of the fundamental OH stretching band and its first overtone have been measured for acetic acid in a series of nonpolar and slightly polar solvents. It is shown that the mechanical anharmonicity of this vibration decreases with increasing dielectric constant of the solvent. An extension of the dielectric model of solute-solvent interaction is proposed to interpret the experimental results.

Infrared spectra of DCl in liquid alkanes

Abstract Preliminary results are reported on the effect of solute-solvent interactions on the form of the DCl fundamental infrared absorption band. It is found that the band shape varies as a function of alkane chain length and isomerism. The results are interpreted in terms of the correlation function for DCl reorientation.

Vibrational anharmonicity of HCl in solution

Abstract The frequencies of the vibrational fundamental and its first and second overtones were measured for HCl in a series of nonpolar and slightly polar solvents. The mechanical anharmonicity, as well as the harmonic frequency, decreased with increasing dielectric constant of the solvent. The experimental results are consistent with a recently proposed extension of the KBM theory of solute-solvent interaction.

Correlations concerning the stretching and bending frequencies of hydrogen-bonded system ≡C-H⃜Y

The hydrogen stretching and bending frequencies, and the corresponding band widths, have been measured for 1-heptyne in the gas phase and in solution in 18 different solvents. The solvents chosen included a number of proton accepting species, as well as several nonpolar molecules. A modified form of the Lippincott model of the hydrogen bond is used to provide a quantitative interpretation of the experimental results.

Solute-solvent interaction in liquids: Moment analysis of infrared absorption bands

Abstract The theory of moment analysis of absorption band shapes is extended to include rotation-translation coupling in a linear solute molecule. It is shown that additional terms arise in the expressions for the even moments. In particular, the square of the average force acting on the solute contributes to the fourth moment because the center of gravity and the center of interaction are not coincident. The force and torque terms are compared quantitatively using a generalized KBM model. Experimental evidence in support of the theory is derived from the Raman spectral data of Perchard et al. [Mol. Phys. 23, 519 (1972)] on HCl and DCl solutions.

On the vibrational symmetry of nonrigid molecules

Abstract A method is described of classifying the normal modes of vibration of nonrigid molecules. Vibrational selection rules for toluene and diphenyl ether are developed in order to illustrate the method.

Temperature dependence of the shape of the infrared absorption fundamental of HCl in solution

Abstract Infrared spectroscopic observations of the temperature dependence of the profile of the rotation—vibration fundamental of HCl in dilute solution in FC-75 (a perfluorinated solvent) are presented. The spectra are analyzed using the method of band moments and the torque resulting from solvent—solute interaction is determined as a function of temperature. The experimental results are compared with those computed using a simple cavity model of the liquid system.

SOLUTE-SOLVENT INTERACTION IN LIQUIDS

The infrared absorption spectra of HCl and DCl in dilute CCl4 have been recorded over a range of temperatures. The band shapes have been analysed using the method of moments, allowing both the rms torque and rms force acting on the solute to be determined as functions of temperature. It is shown that rotation-translation coupling makes a significant contribution to the dynamics of these polar molecules in solution.