Molecular partition function nuclear contributions

Here, represents the contribution of all other internal motions of the molecule to the molecular partition function (rotations, vibrations, electronic and nuclear spin motions). For atomic liquids, this term can be taken as being equal to 1. 

Of course, as we have discussed, the nuclear and electronic degrees of freedom do not contribute to the molecular partition function at ordinary temperatures. For the nuclear term, this is because the two lowest energy levels of the nucleus are separated by an energy of 0(1 MeV). This means that only at temperatures of 0(10 °) K would 1 MeV,... 

Nuclear Spin Contribution. The nuclear spin partition function is the product of the nuclear spin multiplicity 2ij -H 1) for all the atoms in the molecule, where /V is the nuclear spin of the yth atom. Since, apart from processes involving molecular hydrogen and its isotopes (and the transmutation of the elements), nuclear spins are conserved, this contribution is conventionally omitted from the total entropy leaving the practical or virtual entropy (these adjectives are frequently omitted also). 

The material in this chapter is largely organized around the molecular properties that contribute to electron transfer processes in simple transition metal complexes. To some degree these molecular properties can be classified as functions of either (i) the nuclear coordinates (i.e., properties that depend on the spatial orientation and separation, and the vibrational characteristics) of the electron transfer system or (ii) the electronic coordinates of the system (orbital and spin properties). This partitioning of the physical parameters of the system into nuclear and electronic contributions, based on the Born-Oppenheimer approximation, is not rigorous and even in this approximation the electronic coordinates are a function of the nuclear coordinates. The types of systems that conform to expectation at the weak coupling limit will be discussed after some necessary preliminaries and discussion of formalisms. Applications to more complex, extended systems are mentioned at the end of the chapter. 

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