UV photofragmentation of cold Cytosine-M+ complexes (M+: Na+, K+, Ag+)

M. I. TACCONE; A. CRUZ ORTIZ; J. DEZALAY; S. SOORKIA; M. BROQUIER; G. GRÉGOIRE; C. G. SÁNCHEZ; G. A. PINO *

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2019 vol. 123 p. 7744 - 7750

1089-5639

The UV-photofragmentation spectra of cold Cytosine-M+ complexes (M+: Na+, K+, Ag+) were recorded and analyzed through comparison with geometry optimizations and frequency calculations of the ground and excited states at the SCS-CC2/Def2-SVPD level of theory. While in all complexes, the ground state minimum geometry is planar (Cs symmetry), the * state minimum geometry has the NH2 group slightly twisted and an out-of-plane metal cation. This was confirmed by comparing the simulated * Franck-Condon spectra with the vibrationally resolved photofragmentation spectra of CytNa+ and CytK+. Vertical excitation transitions were also calculated to evaluate the energies of the CT states involving the transfer of an electron from the Cyt moiety to M+. For both CytK+ and CytNa+ complexes, the first CT state corresponds to an electron transfer from the cytosine aromatic  ring to the antibonding * orbital centered on the alkali cation. This * state is predicted to lie much higher in energy (> 6 V) than the band origin of the * electronic transition (around 4.3 eV) unlike what is observed for CytAg+ complex for which the first excited state has a nO* electronic configuration. This is the reason for the absence of the Cyt+ + M charge transfer fragmentation channel for CytK+ and CytNa+ complexes.