Atomic Term Symbols

In an atomic term symbol the value of L = 1,2,..., etc. is coded according to spectroscopic notation as 5, P, D,F,G,... etc. (alphabetically for L > 3). Likewise, each atomic state can be characterized by a total electronic spin quantum number S,... 

The numerical value of the quantity 25 + 1 (total multiplicity) is used as a left superscript with the corresponding term code to define the total atomic term symbol, e.g. for L = 2 and 5 = 1, the term symbol is ZD. Closed subshells make no contribution to L and 5 and may be ignored. 

We will see in due course that there are important correlation rules between atomic term symbols and molecular electronic states, rules that are important in understanding both the formation and dissociation of diatomic molecules. Elementary accounts of the theory of atomic structure are to be found in books by Softley [3] and Richards and Scott [4], Among the more comprehensive descriptions of the quantum mechanical aspects, that by Pauling and Wilson [5] remains as good as any whilst group theoretical aspects are described by Judd [6],... 

The magnitudes of these quantities are written as /, L and S, which are known as quantum numbers for each of these quantities, and can be used to specify atomic states through the atomic term symbol... 

The following is wrong with the following atomic term symbols 4Sj and °D1... 

Tlie discussion of atomic structure does not start with the Schrodinger equation, but with the Bohr theory. I believe most students appreciate the opportunity of learning the development of atomic theory in this century and can make the transition from orbits to orbitals without much difficulty. The student can also calculate several important physical quantities from the simple Bohr theory. At the end of the first chapter, there is a discussion of atomic-term symbols in the Russell-Saunders LSMiMs approximation. 

To illustrate one final point, we return to the example of the equivalent configuration, for which the possible atomic term symbols are S, Po,i,2 ... 

Determine the atomic term symbols that may be obtained from the... 

L = 2 atomic term symbol, Ising model interaction constant, diffusion constant... 

Note the ground-state atomic term symbol for Cr is F, which splits into T2, Ti and A2 for an octahedral transition metal complex. For more information regarding term symbol notation and absorption spectra for transition metal complexes, see Shiiver et al. Inorganic Chemistry, 4th ed., W. H. Freeman New York, 2006. http //www.scribd.com/doc/6672586/Electronic-Spectroscopy-l Note excited electrons give off their energy via infrared emission and thermal interactions with the corundum crystal lattice, referred to as electron-phonon (lattice vibrations) interactions. 

As for atoms, term symbols can be defined for diatomic molecules. The term symbols for diatomic molecules are determined similarly to the K quantum number... 

The excited electron in the a antibonding orbital is in a molecular orbital that has 2u symmetry, and the electron still in the tt orbital has Ilg symmetry. The direct product of these two symmetries is simply Hg. (Verify this.) The a and tt electrons can have either the same direction spin or different direction spin (rather, the z components of their spin), so multiplicities of 3 or 1 are possible. Therefore, the term symbols for this excited-state electron configuration are and II states are doubly degenerate. In this case, there are two possible, degenerate tt molecular orbitals for the unexcited electron. Complete term symbols would have values for ft included. For the triplet state, H can be 2,1, or 0. For the singlet state, Q, can only be 1. Unlike atomic term symbols, it is relatively uncommon to see the fi values listed explicitly in the term symbols of diatomic molecules. One would see Ilu to represent all three individual states, rather than Ilu 2> Ilu i, and Ilu o-... 

As with atoms, term symbols are used to designate values of angular momentum quantum numbers for homonuclear diatomic molecules. The scheme is slightly different from the Russell-Saunders scheme that is used for atoms, since L is not a good quantum number. The operator does commute with the electronic Hamiltonian and an energy eigenfunction can be an eigenfunction of Lj ... 

Notice the similarity with the atomic term symbols with the letters S, P, D, and F. 

Find the atomic term symbols for the beryllium associated with the occupancy Is 2si 2pi. 

Find the atomic term symbols associated with an atomic occupancy Is 2s 2p Spi. Find the Russell-Saunders term symbols for the possible states of the oxygen atom with occupancy Is 2s 2p. ... 

Find the atomic term symbol for the ground state of the nitrogen atom. 

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