It turns out that you can’t extrapolate the results of base pairs to whole strands of DNA.

Even though paired bases are connected by weak chemical bonds, it’s the interactions that take place without chemical bonds the interactions between stacked bases that are much more important for dissipating UV energy.

The ability to observe what happens to electronic energy in DNA on such short time scales also extends the hope that methods such as ours can finally determine how DNA is damaged by UV light...

This slow relaxation of energy is utterly different from the mechanism in single bases that transforms the energy into heat in less than a trillionth of a second.

In fact, so much attention has been paid to base pairing that this other interaction, base stacking, has been neglected.