title: Pulsed field ionization electron spectroscopy and molecular structure of aluminum uracil.
abstract: Al-uracil (Al-C4H4N2O2) was synthesized in a laser-vaporization supersonic molecular beam source and studied with pulsed field ionization-zero electron kinetic energy (ZEKE) photoelectron spectroscopy and density functional theory (DFT). The DFT calculations predicted several low-energy Al-uracil isomers with Al binding to the diketo, keto-enol, and dienol tautomers of uracil. The ZEKE spectroscopic measurements of Al-uracil determined the ionization energy of 43 064(5) cm-1 [or 5.340(6) eV] and a vibrational mode of 51 cm-1 for the neutral complex and several vibrational modes of 51, 303, 614, and 739 cm-1 for the ionized species. Combination of the ZEEK spectrum with the DFT and Franck-Condon factor calculations determined the preferred isomeric structure and electronic states of the Al-uracil complex. This isomer is formed by Al binding to the O4 atom of the diketo tautomer of uracil and has a planar Cs symmetry. The ground electronic states of the neutral and ionized species are 2A' ' and 1A', respectively. The 2A' ' neutral state has a slightly shorter Al-O4 distance than the 1A' ion state. However, the 1A' ion state has stronger metal-ligand binding compared to the 2A' ' state. The increased Al-O4 distance from the 2A' ' state to the 1A' state is attributed to the loss of the pi binding interaction between Al and O4 in the singlet ion state, whereas the increased metal-ligand binding strength is due to the additional charge-dipole interaction in the ion that surpasses the loss of the pi orbital interaction.
authors.affiliation: Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors.forename: Serge A
authors.initials: SA
authors.lastname: Krasnokutski
authors.forename: Dong-Sheng
authors.initials: DS
authors.lastname: Yang
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D001665:Binding Sites; D004583:Electrons; D007536:Isomerism; D008024:Ligands; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013057:Spectrum Analysis; D013816:Thermodynamics; D014498:Uracil / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D014498:Uracil; D000535:Aluminum