Molecular dynamics study of the thermodynamic and structural properties of methanol and polarizable/non-polarizable carbon tetrachloride mixtures

Abstract

Molecular dynamics simulations have been performed for methanol/carbon tetrachloride mixtures over the whole composition range at 323 K and zero pressure. The OPLS ͑optimized potentials for liquid simulation͒ potential energy parameters by Jorgensen were used to model the methanol potential. Both a non-polarizable carbon tetrachloride model taken from McDonald, Bounds, and Klein ͓Mol. Phys. 45, 521 ͑1982͔͒ as well as a polarizable model were used. The latter model was devised by combining the model of McDonald, Bounds, and Klein with the atomic polarizabilities proposed by Applequist, Carl, and Fung ͓J. Am. Chem. Soc. 94, 2952 ͑1972͔͒. We show that the role of the methanol-carbon tetrachloride interactions are very important in discussing the thermodynamic mixing properties. In order to reproduce the asymmetric behavior of the excess enthalpies with respect to composition it is necessary to include the non-additive polarization interaction. The structure and especially hydrogen bonding properties are discussed. Radial distribution functions show a strong tendency of methanol to preserve the local order similar to the one in the pure fluid. The deviations from random mixing are more pronounced at the lower mole fractions. This is explained by a frustration model. At low methanol concentrations the molecules get more freedom to align themselves in energetically favorable ͑hydrogen bonded͒ configurations. Throughout the composition range, the majority of the methanol molecules is found to be engaged in two hydrogen bond, As in the pure fluid, this leads to the pattern of hydrogen bonded winding chains. Upon dilution the degree of cross-linking between the chains diminishes whereas the free monomer fraction rises. Furthermore a significant number of the remaining chains close to form cyclic polymers.

Orientational relaxation and vibrational excitation transfer in methanol–carbon tetrachloride solutions

“…8,39 We use the liquid methanol concentration since methanol forms oligomers in CCl 4 with similar short-range structure to that found in liquid methanol. 12 The best fit of the model to the data is shown in Fig. 4, and it gives an R 0 ϭ2.03Ϯ0.04 Å.…”

“…For concentrated methanol in carbon tetrachloride solutions, like those used in the present study, hydrogen bonded oligomers, composed of chains and rings, are the dominant species found in solution. [9][10][11][12] The frequency and width of the hydroxyl stretch depends strongly upon the number of hydrogen bonds formed, making the hydroxyl stretch a sensitive probe of hydrogen bonding in solution. [9][10][11][12][13] The infrared absorption spectra of the solutions studied in the present account appear in Fig.…”

Structural dynamics of hydrogen bonded methanol oligomers: Vibrational transient hole burning studies of spectral diffusion

“…For the concentrated methanol in carbon tetrachloride solutions used in the present study, hydrogen bonded oligomers, composed of chains and rings, are the dominant species found in solution. 20,21 The frequency and width of the hydroxyl stretch absorption band depends strongly on the number of hydrogen bonds formed, making the hydroxyl stretch a sensitive probe of hydrogen bonding in solution. Figure 1 shows the infrared ͑IR͒ absorption spectra of the solution with ͑a͒ and without ͑b͒ the background.…”

“…Methanol molecules that both accept and donate hydrogen bonds in oligomer chains and rings represent the dominant configuration in liquid methanol and at high methanol concentrations in CCl 4 . 20,21 These methanol-d molecules, referred to as ␦, have an absorption peak at ϳ2487 cm Ϫ1 . The shape of the spectrum can be approximated as a Gaussian with a full width at half maximum ͑FWHM͒ of ϳ130 cm Ϫ1 ͓see Fig.…”

Hydrogen Bond Dynamics Probed with Ultrafast Infrared Heterodyne-Detected Multidimensional Vibrational Stimulated Echoes

“…A water molecule can form up to four hydrogen bonds, and the various number and types of hydrogen bonds are not spectroscopically resolvable under the broad hydrogen bonded hydroxyl stretch band [6]. In contrast, molecular dynamics simulations demonstrate that methanol predominantly forms two hydrogen bonds, whether in the pure liquid [8] or as oligomers in CCl 4 [9]. The description of the structure and evolution of hydrogen bonded networks in methanol is greatly simplified compared to water by the preponderance of a single conformation in which each methanol is a single hydrogen bond donor and a single acceptor.…”