Near-degenerate states

Figure A3.13.1 illustrates our general understanding of intramolecular energy redistribution in isolated molecules and shows how these processes are related to intemiolecular processes, which may follow any of the mechanisms discussed in the previous section. The horizontal bars represent levels of nearly degenerate states of an isolated molecule.

Figure A3.13.1. Schematic energy level diagram and relationship between mtemiolecular (collisional or radiative) and intramolecular energy transfer between states of isolated molecules. The fat horizontal bars indicate diin energy shells of nearly degenerate states.

We now consider preferential energy transfer to one or the other of nearly degenerate states in the thiophosgene molecule using an extended five-state... 

We examine the efficiency with which population transfer can be selectively directed by STIRAP -1- FFF control to one of a pair of nearly degenerate states in the presence of background states. The vehicle for our studies is a model of the vibrational spectrum of the nonrotating SCCI2 in Figure 3.6. 

Near-degenerate states lead to oppositely signed terms that occur at nearly the same energy leading to a overall spectral feature that looks like an A term and is called a pseudo-A term (11). In many cases it may be that a quick SOS calculation may be sufficient to describe a pseudo-A term. We have had some success in describing the MCD spectra of furan, pyrrole, and related compounds through this approach (98). 

One of the more well studied collision processes involving Rydberg atoms is collisional angular momentum mixing, or i mixing, the collisional transfer of population among the nearly degenerate states of the same n.28 The process has... 

What are the advantages of the Born Oppenheimer approximation and when is it necessary to go beyond [Separation of electronic and vibrational wavefunctions, existence of PES calculation of IC and ISC rate constants, near-degenerate states]... 

In order to reduce further the uncertainties due to spin-orbit interactions between nearly degenerate states close to the Fermi level Wang el al. [162] proposed a torque method. They illustrated the method by considering a uniaxial system where the energy can be well approximated by... 

In general, the operator S(n) can be chosen such that, through order X", K contains only those terms that couple degenerate or nearly degenerate states. 

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