Molecular dynamics of liquid acetone determined by depolarized Rayleigh and low-frequency Raman scattering spectroscopy

Abstract

Slow to ultrafast dynamics of liquid acetone at variable temperature was investigated by depolarized Rayleigh and low-frequency Raman scattering spectroscopy, in the region 0-200 cm(-1). A detailed analysis was performed on the spectra and corresponding time responses, and a consistent view of the molecular dynamics of this dipolar solvent was obtained. The effects of temperature on the spectra were interpreted, and distinct dynamical processes identified. At very low frequencies, or long time scales, acetone dynamics is characterized by a slow diffusive reorientation obeying the Stokes-Einstein-Debye hydrodynamic theory only in the limit of subslip boundary conditions. An alternative model based on the microviscosity concept proved to be able to reproduce this correlation time and its temperature dependence. A comparative analysis of collective and single-molecule reorientational times, these latter estimated from intramolecular Raman spectra, led to an orientational correlation parameter g(2) of unity, which denotes a statistical disorder of molecular polarizability tensors. A fast local restructuring process is putatively responsible for an additional contribution at subpicosecond time scales often referred to as intermediate response in other molecular liquids. The high frequency portion of the dynamical susceptibility showed the signature of librational intermolecular motions, giving rise to an ultrafast decay of the time correlation function of polarizability anisotropy. The overall approach, which provided valuable information on dynamics, structure and molecular interactions of neat acetone, will be applied to acetone electrolytic solutions.

Effective Fragment Potential-Based Molecular Dynamics Studies of Diffusion in Acetone and Hexane

“…The present work presents the results of molecular dynamics (MD) simulations that assess translational diffusion of both n -hexane and acetone. There have been previous experimental studies of the diffusion , and molecular dynamics of the industrially important acetone. Given the importance and interest of hydrocarbon chain molecules in chemistry, the diffusion of n -hexane is also considered.…”

Low-Frequency Vibrational Modes of Poly(glycolic acid) and Thermal Expansion of Crystal Lattice Assigned On the Basis of DFT-Spectral Simulation Aided with a Fragment Method

“…A low-frequency vibrational spectrum of condensed matter can reflect not only intrinsic molecular structure but also intermolecular structure, which would originate from a balance between thermal motion and van der Waals interactions between molecules, for example, hydrogen bonds and steric hindrance. Hence, vibrational spectroscopy below ∼300 cm –1 has been studied for polymers from viewpoints of stacked and deformed structures of polymer chains and the weak interactions therein, − and for the dynamics and relaxations of molecular aggregates in condensed phases. − Crystalline polymers are attractive targets for far-infrared (FIR) and low-frequency Raman spectroscopies, and thus low-frequency vibrational spectra of various polymer systems have been studied since the 1950s. − Although interpretation in the low-frequency region is not straightforward for polymers, the spectrum can provide valuable information about structures and interactions inside. Recently, THz-Time Domain (THz-TD) spectroscopy has started to be applied to polymer systems. − In our previous studies on a biodegradable polyester, poly-( R )-3-hydroxybutyrate (PHB), ,, a combination of THz-TD and low-frequency Raman spectroscopies and their quantum mechanical simulations revealed that some bands are fairly related to a weak intermolecular hydrogen bonding between CO and CH 3 groups among the PHB chains, as the weak hydrogen bonding had been suggested on the basis of the IR and X-ray experiments. − The hydrogen bonds in PHB were recently confirmed by using new X-ray crystallographic data …”

Ultra-Broadband Dielectric and Optical Kerr-Effect Study of the Ionic Liquids Ethyl and Propylammonium Nitrate

“…71 Third, the OKE spectra of all liquids show a pronounced librational peak in this frequency range, independent of the presence or absence of H bonds. 66,72 Finally, the small increase in S G1 with increasing T is expected for librational motions due to increasing thermal motions, whereas amplitudes usually decrease for vibrations. It should be noted here that although ILs containing pyrrolidinium, tetraalkylammonium, and tetraalkylphosphonium cations exhibit a mode at ∼60 cm −1 that may be associated with interionic stretching vibrations, 73,74 albeit with librational and cross-contributions, this is unlikely to be the source of the G 1 mode for EAN and PAN because the masses of NO 3 − and EtNH 3 + or, respectively, PrNH 3 + , are too small for such a low resonance frequency.…”