Abstract: In this paper, properties of molecular graphs with partly identical topological spectra has been discussed in detail. The concept of pseudo-reflection plane has been described and illustrated by a few examples. The molecular graph G which does not contain the plane of symmetry is said to have a pseudo-reflection plane σ_p if there exists a symmetry plane in a deleting graph G_a′. The G is partitioned into two parts G_(A1)(σ_p), G_(A2)(σ_p) by the plane σ_p. The conjugated species G_(A1)(σ_p)、 G_(A2)(σ_p) are isospectral or partly isospectral molecules if the construction of G_(A1)(σ_p)、G_(A2)(σ_p) are not identical.
In this present article a straight chain containing three vertices has been studied. This graph stands for a general result result of the deletion of numerous partly isospectral molecules.