Threshold ionization of La(C5H8) formed by La-mediated dehydrogenation of 1-pentene

Abstract

La(\chem{C_5H_8}) was formed by La reaction with 1-pentene (CH$_{2}$=CH-CH$_{2}$-CH$_{3}$) in a laser-vaporization supersonic molecular beam source and characterized with mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectrum displays an origin band at 38988 (5) \wn and three vibrational intervals of 130, 294, and 415 \wn. The La(\chem{C_5H_8}) complex is identified as a five-membered metallacycle in C$_{1}$ point group, with the doublet and singlet being the lowest energy states of the neutral and cation, respectively. The energy at 38998 \wn corresponds to the adiabatic ionization energy of the complex, and the three vibration intervals in the order of the frequency increase are assigned to the terminal \chem{CH_3} torsion, asymmetric La-ligand stretch, and symmetric La-ligand stretch excitation of the ion. The La + 1-penetene reaction will also be compared with La reactions with other five-carbon hydrocarbon molecules, such as isoprene, 1-pentyne, and 1,4-pentadiene.