The symmetry properties of a model doublehyphen;stranded polynucleotide, containing only one type of monomer unit, have been investigated by the application of the theory of space groups. The rotational parts of the symmetry operations of such a helix form a group which is isomorphic to the point groupD10, indicating that there is sufficiently high symmetry to make formal treatment by group theory profitable for applications to the molecular dynamics of related helical polymers. A method of developing the irreducible representations of the space group is discussed and some features of the irreducible representations so obtained are described. Electronic spectral properties related specifically to pgr;, pgr;*, andn,pgr;*states are then discussed within the framework of the group theoretical results, particular emphasis being placed on the nature of the exciton bands produced by excitation resonance interaction among the monomer units, selection rules restricting the mixing of states, selection rules for electrichyphen;dipole transitions between the ground state and states of the various exciton bands, and the expected effects of state mixing on the electronic spectral intensities of transitions to pgr;, pgr;*, andn,pgr;*exciton bands.
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