Fragmentation patterns of core-ionized thymine and 5-bromouracil

Area of Science:

• Physical Chemistry
• Atomic and Molecular Physics
• Chemical Physics

Background:

• Pyrimidine bases like thymine are fundamental to DNA.
• Understanding their behavior under radiation is crucial for radiation biology and materials science.
• Core ionization can lead to complex fragmentation patterns.

Purpose of the Study:

• To investigate the photofragmentation of thymine and 5-bromouracil following core ionization.
• To compare fragmentation channels between thymine and 5-bromouracil, and assess the effect of functional group substitution (bromination/deuteration).
• To correlate experimental fragmentation data with theoretical calculations.

Main Methods:

• Utilized the photoelectron-photoion-photoion coincidence (PEPIPICO) technique.
• Studied photofragmentation induced by soft x-ray core ionization (C 1s).
• Employed deuterated thymine and 5-bromouracil samples for fragment identification and compared experimental results with ab initio unrestricted Hartree-Fock calculations.

Main Results:

• Identified dominant fragmentation channels for thymine and 5-bromouracil.
• Observed that fragmentation pathways are largely identical between thymine and 5-bromouracil, indicating functional group substitution has minimal impact on major fragmentation routes.
• Determined relative intensities of fragmentation channels and compared them with calculated appearance energies.

Conclusions:

• The core ionization of thymine and 5-bromouracil leads to similar fragmentation patterns.
• The molecular structure and fragmentation dynamics are conserved despite bromination or deuteration.
• Experimental findings align well with theoretical predictions of fragmentation energies.