Ground-state term, atomic molecular

Figure 5.3 Correlation diagram of molecular terms for a pair of similar (excited and ground-state) alkali atoms. The right part of the figure corresponds to free atoms, the left part corresponds to the strong dipole-dipole interaction (Fdip A ). Dots mark crossings of terms coupled by the Coriolis interactions.

Calculate the value of the molecular partition function of CI2 gas at 298.15 K and a pressure of 1.000 bar. Find the Russell-Saunders term symbol for the ground-state of atomic chlorine and find the degeneracy of this level. Assume that the electronic partition function can be approximated by go> the degeneracy of the ground-level. 

Values of ag, are not very difficult to calculate, for Eq. (1) involves only ground-state wave functions. Furthermore, Flygare and Goodisman (25) have shown that Eq. (3) gives values of aa that are reasonably accurate (within 1 to 2 ppm), using tabulated values of the free atom (Lamb) term (7, 55, 56) and a knowledge of the molecular geometry ... 

Energy levels of heavy and super-heavy (Z>100) elements are calculated by the relativistic coupled cluster method. The method starts from the four-component solutions of the Dirac-Fock or Dirac-Fock-Breit equations, and correlates them by the coupled-cluster approach. Simultaneous inclusion of relativistic terms in the Hamiltonian (to order o , where a is the fine-structure constant) and correlation effects (all products smd powers of single and double virtual excitations) is achieved. The Fock-space coupled-cluster method yields directly transition energies (ionization potentials, excitation energies, electron affinities). Results are in good agreement (usually better than 0.1 eV) with known experimental values. Properties of superheavy atoms which are not known experimentally can be predicted. Examples include the nature of the ground states of elements 104 md 111. Molecular applications are also presented. 

The Politzer-Parr partitioning of molecular energies in terms of atomic-bke contributions results in an exact formula for the nonrelativistic ground-state energy of a molecule as a sum of atomic terms that emphasizes the dependence of atomic and molecular energies on the electrostatic potentials at the nuclei. 

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