Vibrational relaxation in liquids

A new theory is presented for vibrational energy relaxation in a liquid. It is shown that a vibrationally excited probe molecule relaxes through interaction with the density fluctuations in the surrounding solvent fluid. This interaction occurs through a potential V(k), which is expressed in terms of the intermolecular force between the excited probe molecule and the surrounding fluid molecules. By assuming spherically symmetric solvent particles the T ₁ energy relaxation time for direct V-T processes is related to the translational dynamic structure factor for the fluid S(k, ω_v), evaluated at the vibrational resonance frequency. It is shown that this is described by gas-like particle motions on a very short distance scale corresponding to k vectors lying well beyond the first or second peaks of the fluid structure factor S(k). Such motions can be pictured as high-frequency, short-distance distortions of the local equilibrium configuration of the solvent particles around the probe. T ₁ ^-1 is found to be proportional to ρ_e T ^1/2 ω_v ^-3. The V-V energy exchange relaxation time is also calculated. This is found to be proportional to S(k, ω′) evaluated at a frequency ω′, corresponding to the vibrational energy missmatch. An energy gap law for the V-V process is derived.     

Vibrational relaxation study in carbonyl containing molecule: role of hydrodynamic and dispersion forces

The isotropic Raman component of the C = O stretching mode of ethyl acetate (EA) was analyzed using various polar and nonpolar solvents. It was found that the bandshape approaches towards Lorentzian at high dilution using the curve‐fitting method. The isotropic Raman band was also analyzed by estimating the correlation coefficient with reference to the Lorentzian lineshape using a simple method of linear‐curve fitting. The effects of dispersion and hydrodynamic forces on bandwidth were studied in details. The vibrational relaxation rate was studied using certain parameters and it was found that the microscopic based parameter can explain the complexities occurring in solute–solvent interactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Vibrational frequency correlation and vibrational dephasing in aqueous nitrate solutions

The vibrational frequency correlation functions

of the v ₁(A′₁) mode of NO₃ ^- ions in aqueous NH₄NO₃ solutions are calculated directly from isotropic Raman profiles, assuming that the process ω(t) is gaussian. The calculated correlation functions are oscillatory decaying functions with a time period of about 0·35 ps. A model based on the generalized Langevin theory is proposed and a theoretical correlation function, obtained by first-order truncation of Mori's continued fraction representation, is found to reproduce both the observed vibrational frequency correlation functions and the vibrational correlation functions. The observed short-time oscillation with a frequency of about 95 cm^-1 is attributed to an inter-molecular librational motion between a NO₃ ^- ion and surrounding water molecules and cations.     

Vibrational dephasing of spherical top anions in aqueous solutions

The vibrational dephasing times for spherical top anions in aqueous solutions calculated from in the shape of the isotropic Raman bands of the fully symmetric vibrations of anions, depending on the temperature and the nature of the anion, are analyzed. It is concluded that the dephasing rates for the anions and their temperature dependences can be reasonably explained within the framework of a model that describes the vibrational dephasing of a diatomic molecule interacting with a solvent molecule by using the Morse potential.     

Regularities and similarities in plasma broadened spectral line widths (Stark widths)

Regularities and similarities in plasma broadened line widths have been studied by a comprehensive analysis of existing experimental data. Regularities are expected on the basis of general atomic structure considerations, and should be evident for spectral series, for corresponding transitions in homologous atoms and in isoelectronic sequences. Furthermore, similarities of line widths are expected for multiplets, supermultiplets and, to a lesser degree, for transition arrays. A comprehensive examination of literature data has been undertaken, which shows generally a close adherence of the measured data to the expected regularities. A few notable exceptions are also given.     

Multipoles and rotational relaxation in liquids

The role of multipolar interactions in quenching free rotation in condensed phases is discussed, with particular attention paid to the HCl-SF₆ system. The magnitude of these interactions is shown to be closely correlated with the dielectric loss of the solvent, and to be sufficient to explain at least partially the variations of linewidth in the HCl rotational spectrum.     

Vibrational relaxation study in 4-chloroacetophenone

Vibrational relaxation process has been emerged as a useful tool in probing the nature of solute solvent interactions in liquid phase. The Laser Raman techniques have been used to study the vibrational and rotational frequencies of molecules, which provide detailed information about the dynamic processes involved in liquids. Raman spectra of C=O stretching mode of 4-chloroacetophenone dissolved in acetonitrile and chlorobenzene have been recorded as a function of solvent concentration ranging from 10% to 90% concentration at room temperature. The 4-chloroacetophenone is a molecule having wide application in manufacture of drugs, perfumes and cosmetics. This study may provide useful information about the vibrational relaxation mechanisms in liquid solutions at molecular level. The Laser Raman components were determined and the spectra were analyzed at different solvent concentrations. The theoretical models have been tested and compare with the experimental results.     

Phase transition in liquids with directed intermolecular bonding

Liquids with quasi-chemical bonding between molecules are described in terms of vertex model. It is shown that this bonding results in liquid–liquid phase transition, which takes place between phases with different mean density of intermolecular bonds. The transition may be suggested to be a universal phenomena for those liquids.     

Solvation forces in branched molecular liquids

The solvation force of squalane confined between a silicon tip and a graphite surface has been measured by atomic force microscopy. This highly branched molecule shows oscillatory force profiles similar to those of spherical and linear chain molecules. Squalane molecules closest to the substrate are tightly bound and finer details imply that interdigitation occurs. This agrees with computer simulations for branched molecules but differs qualitatively from force balance experiments. These differences arise from the smaller confinement area and the different chemical nature of the surfaces.     

Vibrational relaxation processes and molecular form factors

A theory that relates collision matrix elements for vibrational/rotational transfer processes between molecular systems to molecular form factors is presented.     

Control of light by electromagnetic forces on conductive liquids

An electrical current passed through a conducting liquid located in a magnetic field causes a relatively large movement of the liquid. By choosing a liquid with either suitable absorptive, reflective, refractive, optical rotation or light scattering properties, the electromagnetically induced movement can be used as the basis of many electrically controlled light devices. These include light valves, deflectors and variable f mirrors. While limited to msec speed, the electromagnetic light control device has the important advantages of simplicity, reliability, high light transmission and contrast ratio.     

Heterogeneous relaxation patterns in supercooled liquids studied by solvation dynamics

We have measured the solvation dynamics of a dipolar supercooled liquid near its glass transition in a temperature range in which the average structural relaxation time varies more than four orders of magnitude. The analysis of the time dependent average emission energy and the inhomogeneous linewidth of the S0<--T1(0-0) transition reveals that the orientation correlation decay pattern intrinsic in each relaxing unit is associated with a stretching exponent beta(intr)=1.00+/-0.08 in the entire range T(g)(KWW) the individual time constants remain correlated to their initial values at t=0.