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Updated: Jun 20, 2026

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation
Published on: October 30, 2012
Initial excited-state structural dynamics of uracil from resonance Raman spectroscopy are different from those of
Soujanya Yarasi1, Susan Ng, Glen R Loppnow
1Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Abstract:
To explore the origin of the differences in UV photochemistry of uracil (RNA) and thymine (DNA) nucleobases, we have measured the UV resonance Raman spectra of uracil in aqueous solution at wavelengths throughout the lowest-energy absorption band and analyzed the resulting resonance Raman excitation profiles and absorption spectra using a time-dependent wave-packet formalism to obtain the initial excited-state structural changes. In contrast to thymine, which differs from uracil only by the presence of a methyl group at C(5), most of the resonance Raman intensity and resulting initial excited-state structural dynamics for uracil occur along in-plane hydrogen-bond angle deformation, ring stretching, and carbonyl vibrational modes. Weaker intensities and less significant structural dynamics are observed along the C=C stretching mode. These results suggest that the initial excited-state structural dynamics of uracil occur along a carbon pyramidalization coordinate. These dynamics are different from those of thymine, which distorts primarily along a C(5)=C(6) bond lengthening coordinate. These differences in initial excited-state structural dynamics can explain the different primary photoproducts observed for these two pyrimidine nucleobases.
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