Arie Bar-Haim

On mean residence and first passage times in finite one-dimensional systems

We present a simple derivation of mean residence times (MRTs) and mean first passage times (MFPTs) for random walks in finite one-dimensional systems. The derivation is based on the analysis of the inverse matrix of transition rates which represents the random walk rate equations. The dependence of the MRT and of the MFPT on the initial condition, on the system size, and on the elementary rates is studied and a relationship to stationary solutions is established. Applications to models of light harvesting by supermolecules, and of random barriers, and to relaxation in the Ehrenfest model are discussed in detail. We propose a way to control the MFPT in supermolecules, such as dendrimers, via molecular architecture.

Dendrimers as light harvesting antennae

We consider energy transfer from an initially excited state on a dendrimer to a trap located at its center. The energy transfer process is dominated by an inherent geometric bias. We propose that dendrimers can serve as efficient artificial antenna systems for light harvesting. Based on mean first passage time calculations, we demonstrate that the effective rate of capture by the trap depends on the size of the dendrimer, the coordination number, the rates of migration, and the initial condition. The efficiency of the system increases rapidly when an energetic funnel is added, which competes with the geometric bias.

Widening the alkyl hypofluorite family. On the existence of ethyl hypofluorite

Abstract Unlike methanol and t-butanol, most other alcohols do not form alkyl hypofluorites when reacting with fluorine, since immediate HF elimination takes place even at low temperatures. Notable exceptions to this trend are the two deuterated ethanols CD 3 CD 2 OD and CH 3 CD 2 OH, which do produce the corresponding hypofluorites. Their identification and some of the reasons for this exclusive behavior are outlined.