Resonant Channel Coupling in Electron Scattering by Pyrazine

Detailed investigation of the three low-energy resonances seen in electron scattering by the diazabenzene molecule pyrazine reveals that the first two are nearly pure single-channel shape resonances, but the third is, as long suspected, heavily mixed with core-excited resonances built on low-lying triplet states. Such resonant channel coupling is likely to be widespread in $\pi$-ring molecules, including the nucleobases of DNA and RNA, where it may form a pathway for radiation damage.

Figure 1

Structure of the pyrazine molecule. Nitrogen is blue (light), carbon brown (dark), and hydrogen white.

Figure 2

Occupied and vacant $\pi$ molecular orbitals of pyrazine involved in the formation of low-energy electron-scattering resonances.

Figure 3

Partial cross sections for electron-pyrazine scattering in the resonant ${}^{2}B_{2g}$ symmetry obtained with different treatments of polarization (see text for discussion). The horizontal bar shows the measured resonance position (Ref. 8).

Figure 4

Partial cross sections for electron-pyrazine scattering in the ${}^{2}B_{3u}$ and ${}^{2}A_u$ symmetries (see text for discussion). The horizontal bars (gray for ${}^{2}A_u$ and black for ${}^{2}B_{3u}$) show the measured resonance positions (Ref. 8).