Subject: ET theory/Electronic coupling

From: "Hui-Hsu (Gavin) Tsai" <[email-masked]>
Date: Thu, 1 Mar 2001 12:09:02 -0500

Dear CCLers and Silmar:

       Thanks for Silmar's email. It is very helpful.

       The two assumptions Silmar pointed out answer part of my questions.
      
** [The most common electron transfer theories use the two
         following assumptions:
        (i) The electronic coupling(Tab) is >> than the other therms.
        (ii) Tab(Q)=Tab(Q*), i.e, the value of Tab is constant and is
             equal to the one obtained for the transition state (TS).]**

      From Marcus theory, the factors which can affect ET rate are electronic
coupling,  temperature, driving force (G), and reorganization energy. Some
researches are mainly focused on the theoretical calculations (superexchange
and NBO analysis) of electronic coupling. (Newton, Ratner, Curtiss, Miller,
Paddon-Row...)
(Maybe) Due to these two assumptions, the other factors are ignored.
The one interesting point in these researches is most of the calculated 
data are not compared with experimental results. As usual, most theoretical
calculations are compared with well-known results to assess the quality.

   The another interesting question is different experimental methods.
 They are several spectroscopic methods are used to measure the ET rate such 
as time-resolved fluorescence, ultrafast absorption different
spectroscopy, and transient absorption...
I even think some measured rates are not involved with the nuclear 
reorganization and solvent reorientation
and the electronic coupling dominates the rate due to the fast time scale. 
There are also some different kinds of electron transfer such as pohotinduced
excited state electron transfer and gound state charge/hole hopping.
 I also think different measurement of different kinds of electron transfer 
shall require different theoretical approaches. But the concepts are not
clear for me.

   I am just the beginner of this field. Any discussion and comment are
valuable, welcome, and appreciated.

Gavin