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Metal-pyridine (metal=Li, Ca, and Sc) complexes are produced inlaser-vaporization molecular beams and studied by pulsed-field-ionization zero-electron-kinetic-energy (ZEKE) spectroscopy and theoretical calculations. Both σ and π structures are considered for the three complexes by theory, and preferred structures are determined by the combination of the ZEKE spectra and calculations. The Li and Ca complexes prefer a σ bonding mode, whereas the Sc complex favors a π mode. Adiabatic ionization energies and metal-ligand vibrational frequencies are determined from the ZEKE spectra. Metal-ligand bond dissociation energies of the neutral complexes are obtained from a thermodynamic cycle. The ionization energies follow the trend of Li-pyridine (32 460 cm-1)≤Ca-pyridine(39 043 cm-1)≤Sc-pyridine(42 816 cm-1), whereas the bond energies are in the order of Ca-pyridine (27.0 kJ mol-1)≤Li-pyridine(49.1 kJ mol-1)≤Sc-pyridine(110.6 kJ mol-1). The different bonding modes between the main group metals and transition element are discussed in terms of Sc 3d orbital involvement. The bond energy differences between the Li and Ca metals are explained by the number of valence s electrons and the size of the metal atoms. [ABSTRACT FROM AUTHOR]

Neodymium (Nd) complexes of benzene and naphthalene were synthesized in a laser-ablation supersonic molecular beam source. High-resolution electron spectra of these complexes were obtained using pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy. Second-order Mo\ller-Plesset perturbation calculations were employed to aid spectral and electronic-state assignments. The adiabatic ionization energies were measured to be 38 081 (5) cm-1 for Nd(benzene) and 37 815 (5) cm-1 for Nd(naphthalene). For the Nd(benzene) complex, the observed frequencies of 831 and 286 cm-1 were assigned to C-H out-of-plane bending and Nd+-C6H6 stretching modes in the 6A1 ion state and 256 cm-1 to the Nd-C6H6 stretching mode in the 7A1 neutral state. To confirm these assignments, the ZEKE spectrum of the deuterated species was recorded, and the corresponding vibrational frequencies were measured to be 710 and 277 cm-1 in the ion state and 236 cm-1 in the neutral state. For the Nd(naphthalene) complex, the observed vibrational modes were C10H8 bending (394 cm-1), Nd+-C10H8 stretching (286 and 271 cm-1), Nd+-C10H8 bending (80 cm-1), and C10H8 twisting (105 cm-1) in the 6A′ ion state and metal-ligand bending (60 cm-1) and ligand twisting (55 cm-1) in the 7A′ neutral state. The formation of the ground state of the Nd(benzene) complex requires 4f → 5d and 6s → 5d electron excitation of the Nd atom, whereas the formation of the ground state of Nd(naphthalene) involves the 6s → 5d electron promotion. [ABSTRACT FROM AUTHOR]

Al-thymine (Al–C4H3N2O2CH3) is produced by laser vaporization of a rod made of Al and thymine powders in a molecular beam and studied by single-photon pulsed-field ionization-zero electron kinetic energy (ZEKE) photoelectron and IR-UV resonant two-photon ionization spectroscopy and density functional theory calculations. The ZEKE experiment determines the adiabatic ionization energy of the neutral complex and 22 vibrational modes for the corresponding ion with frequencies below 2000 cm-1. The IR-UV photoionization experiment measures two N–H and three C–H stretches for the neutral species. The theoretical calculations predict a number of low-energy isomers with Al binding to single oxygen or adjacent oxygen and nitrogen atoms of thymine. Among these isomers, the structure with Al binding to the O4 atom of the diketo tautomer is predicted to be the most stable one by the theory and is probed by both ZEKE and IR-UV measurements. This work presents the first application of the IR-UV resonant ionization to metal-organic molecule systems. Like ZEKE spectroscopy, the IR-UV photoionization technique is sensitive for identifying isomeric structures of metal association complexes. [ABSTRACT FROM AUTHOR]