The transient solvation of a polar fluorescent probe has been studied by the time resolved Stokes shift technique with roughly five times shorter time resolution than previously reported. New shorter time components in the solvation relaxation function C(t) have been discovered for methanol, propionitrile, and propylene carbonate; the C(t) function for acetonitrile is singly exponential within the limitations of the instrument. The observed C(t) has been compared to theoretical calculations using the dielectric continuum (DC) model for each solvent, with non‐Debye expressions for the solvent dielectric response. For methanol the DC model predictions agree closely with experiment. For the polar aprotic solvents propylene carbonate and propionitrile, the shape of the experimental decay is different from the DC predictions, but the average decay times 〈τs〉 are closer to the DC predictions than previously reported. The comparison of theory and experiment is clearly limited by the inconsistencies and limited f...

Femtosecond resolved solvation dynamics in polar solvents

Nonexponential solvation dynamics of simple liquids and mixtures

Influence of solvent reorientation dynamics upon the kinetics of some electron-exchange reactions

The characteristics of the rotational‐vibrational relaxation of acetonitrile, benzonitrile, 2‐propanol, and p‐dioxane were observed by determining the correlation functions of several infrared and Raman rotation‐vibration bands of these liquids. Benzonitrile and 2‐propanol were also investigated as dilute solutions in CCl4 and in CS2, whereas p‐dioxane was also observed in solution with a variety of electron‐donating, electron‐accepting (among them chloroform, water), and nonpolar molecules. The results show that the intermolecular forces need about 0.1 × 10−12–0.2 ×−12 sec to cause an observable effect on the molecular motion. Regardless of the polarity or association of the liquids or solutions investigated, rotational relaxation is the predominant mode of decay for times less than 0.5 × 10−12 sec after the onset of observation: The C≡ N stretch of benzonitrile and the investigated modes of p‐dioxane are, probably, exceptions. It is also shown that the vibrational correlation functions do not decay pure...

Molecular Motion in Liquids: Rotational and Vibrational Relaxation in Highly Polar and Strongly Associated Systems

The consequences of non‐Debye solvent relaxation upon the barrier‐crossing dynamics of adiabatic electron‐transfer processes have been explored numerically using a rate formulation due to Hynes for several common forms of the dielectric response function E(s), with the objective of assessing the likely experimental importance of such effects. For the ‘‘multiple Debye’’ form of E(s), analytic expressions for the required time‐correlation function can be obtained, whereas for the Davidson–Cole and Cole–Cole forms numerical solutions to the inverse Laplace transform were required. Illustrative numerical results are presented of the increases in the adiabatic barrier‐crossing frequency, νn, predicted to be engendered by the presence of higher‐frequency relaxation components for dielectric conditions of likely experimental relevance. Substantial (five‐ to ten fold) rate enhancements are often obtained, resulting from the disproportionately large influence upon νn predicted to arise from the higher‐frequency ...

Solvent dynamical effects in electron transfer: Predicted consequences of non‐Debye relaxation processes and some comparisons with experimental kinetics

Dielectric constants and losses have been measured at wavelengths of 3 × 104, 10.0, 3.22, 1.96, and 1.25 cm at 30°C for pure acetonitrile, pure propionitrile, five mixtures of acetonitrile and benzonitrile and three mixtures of propionitrile and benzonitrile. A single relaxation time of 3.3 × 10–12 s has been obtained for pure acetonitrile, whereas the dielectric data of pure propionitrile indicate an unsymmetrical distribution of relaxation times in good agreement with the Davidson-Cole representation. The dielectric data of the binary mixtures of acetonitrile and benzonitrile have been analyzed in terms of two partly superimposed Deby e regions, whereas that of propionitrile and benzonitrile have been interpreted in terms of three partly overlapping Debye regions.

Dielectric relaxation in the mixtures of some nitriles

The complex dielectric permittivity of ortho-, meta-, and para-chloroaniline has been measured at various temperatures at the wavelengths of 10, 3, 2, and 1 cm. For the first two compounds the measurements have been made in pure liquid from as well as in solutions in carbon tetrachloride at various concentrations. p-Chloroaniline has been measured only in dilute solution form. The results have been analyzed in terms of two relaxation times, attributed to the rotation of the entire molecule and to the inversion of the NH2 group. Evidence for the self association of the molecules through weak hydrogen bonding has been indicated.

Jaakko K. Eloranta

Papers

Dielectric relaxation in the mixtures of some nitriles

Dielectric relaxation in three chlorine substituted anilines

Dielektrische relaxation in gemischen einiger nitrile