Vertical attachment energies

Among the nudeobases, Thy and Cyt are most readily reduced (Table 10.2). Electron attachment energies have been determined in the gas phase (Aflatooni et al. 1998), and they confirm this view. Theoretical vertical attachment energy calculations rank the nudeobases in the order Ura < Thy < Cyt < Ade < Gua (Sevilla et al. 1995). 

VAEs, See Vertical attachment energies (VAEs) Valley-ridge inflection (VRI) points, 39... 

VDEs, See Vertical detachment energies (VDEs) Vertical attachment energies (VAEs), 80 Vertical detachment energies (VDEs), 80 Vibrational spectroscopy, 66 Vicens and Westhof model system, 152 Voodoo graphics chip (1996), 5... 

Concerning the shift in the energy position of the NIS, it is instructive to refer to Fig. 16 which shows schematically the vertical attachment energy (VAE), the electron affinity (EA) and the vertical detachment energy (VDE) and to Fig. 17 which shows schematically the increase in the VAE (less negative) and the increase in the EA (more positive) in going from dilute gas to the liquid. 

Fig. 16. Schematic potential energy diagrams for AX and AX indicating the electron affinity EA, the vertical attachment energy VAE, and the vertical detachment energy VDE. 

From ETS experiments (Aflatooni et al. 1998), Aflatooni et al. showed that energies required to attach an electron into the lowest empty valence molecular orbitals of all the bases are positive. This means that all the bases have negative valence vertical electron affinity (<0). The vertically formed anions of pyrimidines bases (C, T, and U) were found to be more stable than the purines (G and A) by ca. 0.2 eV. The ETS spectra of U, T, C, G, and A are shown in O Fig. 34-7. The spectra in O Fig. 34-7 arise due to the occupation of the lowest empty 7t -MOs of the parent molecules by the electron. The vertical lines on the spectra (O Fig. 34-7) show the position of the vertical attachment energies. For guanine anion, the ETS (shown in O Fig. 34-7) was observed for its enol tautomer (for details see Aflatooni et al. [1998]). For each of these molecules, three VAEs, associated with the three lowest vacant tTi, tT2, and 7T3 MOs, were determined. The VAEs 0.22,1.58, and 3.83 eV for uracil 0.29,1.71, and 4.05 eV for thymine 0.32,1.53, and 4.50 eV for cytosine 0.54,1.36, and 2.17 eV for adenine and 0.46,1.37, and 2.36 eV for guanine(enol) tautomer were determined by ETS. 

Experimental (ETS) and theoretical vertical attachment energies (VAEs) in uracil and the DNA bases ... 

The AEA is also depicted pictorially in Figure 1, as is the vertical attachment energy (VAE), which is defined analogously to the VDE but starting from the ground state of the neutral molecule ... 

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