  We report on a study of the interactions between holes and molecular
vibrations on dry DNA using photoinduced infrared absorption spectroscopy.
Laser photoexcited (PE) holes are found to have a room-temperature lifetime in
excess of 1 ms, clearly indicating the presence of localization. However, from
a quantitative model analysis of the frequency shifts of vibrational modes
caused by the PE holes, we find the holevibrational coupling constant to be
relatively small, 0.2. This interaction leads to a change in the conformational
energy of 0.015 eV, which is too small to cause selftrapping at room
temperature. We conclude that, at least in the dry (A) form, DNA is best
understood in terms of a double chain of coupled quantum dots arising from the
pseudo-random chain sequence of base pairs, in which Anderson localization
prevents the formation of a metallic state.
