Canonical transformation method in the thermodynamics of a partially ionized plasma

A study is made of a system of interacting fermions under conditions when pair bound states can be formed. A canonical transformation that contains Fermi and Bose operators is proposed to describe these states. After the transformation the original Hamiltonian is expressed in terms of these new operators. In the case of a rarefied gas the transformed Hamiltonian describes a mixture of a perfect gas of bosons and fermioas whose interaction is described by a certain renornmlized potential. When applied to the thermodyaamics of a partially ionized plasma it is shown that allowance for this interaction leads to expressions that do not contain divergences. A convergent expression is obtained for the partition function of the atoms.