linear molecules with a center of symmetry, the X2 molecules (Fig. 3.14eg ), possess plane and an infinite number of C2 axes principal axis and thus have Dnh symmet linear molecules with a center of symmetry, such as BeF2 and all of the X2 molecules (Fig. 3.14e-g), possess a horizontal mirror plane and an infinite number of C2 axes perpendicular to the principal axis and thus have Dnh symmetry. Exercise: If the triphenylphosphin molecule were planar, what would be its point group? linear molecules with a center of symmetry, the X2 molecules (Fig. 3.14eg ), possess plane and an infinite number of C2 axes principal axis and thus have Dnh symmet linear molecules with a center of symmetry, such as BeF2 and all of the X2 molecules (Fig. 3.14e-g), possess a horizontal mirror plane and an infinite number of C2 axes perpendicular to the principal axis and thus have Dnh symmetry. Exercise: If the triphenylphosphin molecule were planar, what would be its point group