Possibility of distinguishing DNA bases and of tracking the keto–enol tautomerism by using high-order harmonic generation

We point out the possibility to distinguish the DNA bases (adenine, cytosine, guanine and thymine) by using the high-order harmonics sources. Moreover, we find the intensity peaks of the high-order harmonics emitted by thymine base while this molecule is near the stable states (keto and enol) as well as at the transition state along the chemical reaction path of a tautomerism. This finding shows the possibility of tracking the DNA tautomerism. Our investigation is based on the simulation method. The structures of four DNA bases and the keto–enol tautomerism of thymine are simulated by the molecular dynamics method within the Born–Oppenheimer approximation. High-order harmonics, emitted from the bases while molecules are exposed to ultrashort laser pulses are calculated by the strong-field approximation within the Lewenstein model. The calculated data then are used as ‘experimental’ high-order harmonics sources for investigation.