Initial excited-state structural dynamics of thymine are coincident with the expected photochemical dynamics

To explore the excited-state structural dynamics of thymine, a DNA nucleobase, we measured the resonance Raman spectra of thymine in aqueous solution at wavelengths throughout the lowest-energy absorption band. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism yielded the excited-state structural dynamics. The photochemically relevant C=C stretching and C-H deformation vibrational modes were found to exhibit maximum resonance Raman intensity and structural change upon photoexcitation for thymine, suggesting that the initial dynamics of thymine lie along the photochemical reaction coordinate.