Brief comments on perturbation theory of a nonsymmetric matrix: The GF matrix

Perturbation theory for nonsymmetric matrices is discussed for the GF matri x for molecular vibrations. As a simple extension of early results, two app roaches are given: one a direct diagonalization of the nonsymmetric matrix, the other a presymmetrization. Presymmetrization of the GF matrix, well kn own for DeltaF, is also described here for DeltaG. It permits the use of st andard perturbation theory for symmetric matrices. Application of the secon d-order expression for the DeltaG case to the determination of the frequenc ies of many ozone isotopomers is given elsewhere.