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

- Simulating the structure of DNA bases and a tautomerism of thymine.
- Calculating the HHG spectra from DNA bases.
- Four bases are distinguish into two groups: adenine, guanine and cytosine, thymine.
- Keto-enol tautomerism in thymine may be probed by the HHG spectra.

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.