Viscosity dependence of geminate recombination efficiency after bimolecular charge separation

Abstract

Photodynamics in superfluid helium: Femtosecond laser-induced ionization, charge recombination, and preparation of molecular Rydberg states A subpicosecond pump-probe laser study of ionization and geminate charge recombination kinetics in alkane liquidsThe efficiency of geminate recombination after bimolecular ionization of an excited electron donor ͑or acceptor͒ is studied. For ions starting from inside or outside the recombination layer, the recombination efficiency has the opposite viscosity dependence. As a result the latter becomes nonmonotonous, provided the kinetic controlled ionization gives way to a diffusional one, creating the more remote ions the higher the solvent viscosity. This effect, first discovered experimentally, receives its explanation here, which is conceivable only on the basis of the Integral Encounter Theory of remote electron transfer in the liquid state.

The Rehm–Weller Experiment in View of Distant Electron Transfer

“…[32][33][34][35] A great deal of recent experimental work focuses on the distance distribution of the reaction partners. [36][37][38][39][40] Upon increasing the reaction exergonicity, the reaction layer changes from contact to remote, whereby a high reaction rate is retained. In a recent publication, Burshtein and Ivanov [19] have point-Abstract: The driving-force dependence of bimolecular fluorescence quenching by electron transfer in solution, the Rehm-Weller experiment, is revisited.…”

Contact and Distant Luminescence Quenching in Solutions

“…Finally, the excitation becomes the unique reaction product since the recombination to the ground state is switched off. Being calculated with (81), which accounts for the transfer reversibility (ionization of excited state), this function appears to be different from the simplest ones, (82) and (83), suited for irreversible recombination. Shown in Figure 11 these functions, although they are different, resemble the experimental results obtained in [57][58][59].…”

“…Keeping it the same, the bell-shaped curve is sometimes substituted by the rectangular one [16,81,82].…”

Influence of the excitation light intensity on the rate of fluorescence quenching reactions: pulsed experiments

“…Such is the influence that for the lower channels of the reaction in the MIR, the maximum of the reactivity is shifted away from contact creating a layer of strong recombination probability few Angstroms away from the contact distance s. 2 This effect has been shown experimentally. 3,4 The solvent relaxation time expression is as follows:…”

“…2 Experimental scrutiny of these theories is only now being performed. [3][4][5][6][7] It has been shown how the viscosity and the magnetic field modulate reactions. For example, it has been observed that recombination efficiency depends on the viscosity of the medium non-monotonically as a combined effect of the molecular transport and the spatial characteristics of the electron transfer reactions.…”