Possibility of tracking imino-amino tautomerism of cytosine by ultra-short laser pulses using high-order harmonic generation

► We calculate high harmonic spectra of cytosine, which is one of DNA bases. ► The alignment dependence of HHG tells us about the tautomer states. ► We calculate high harmonic spectra in a chemical reaction path of tautomerization. ► The HHG intensity peaks near the stable and the transition states. ► This finding could serve as a useful tool for tracking the tautomerism.