DEHYROGENATION OF ETHYLENE: SPECTROSCOPY AND STRUCTURES OF La(C$_2$H$_2$) AND La(C$_4$H$_6$) COMPLEXES

Abstract

Hydrogen elimination is observed in the reaction of laser-ablated La atoms and ethylene (C$_2$H$_4$) in a pulsed molecular beam source. Dehydrogenated products, La(C$_2$H$_2$) and La(C$_4$H$_6$), are identified by time-of-flight mass spectrometry and studied by pulsed-field-ionization zero-electron kinetic energy spectroscopy and density functional theory calculations. La(C$_2$H$_2$) is determined as a triangle (C$_{2v}$) in the $^2$A$_2$ ground electronic state, where La binds with C$_2$H$_2$ in a two-fold mode ($\eta^2$). La(C$_4$H$_6$) is identified as a diligand species with La being sandwiched between C$_2$H$_2$ and C$_2$H$_4$, each in a two-fold binding mode, and the complex is in the $^2$A$_1$ ground electronic state. The adiabatic ionization energies of La($\eta^2$-C$_2$H$_2$) and La($\eta^2$-C$_2$H$_2$)($\eta^2$-C$_2$H$_4$) are measured to be 41174(5) and 39405(5) cm$^{-1}$, respectively. La$^+$-C$_2$H$_2$ and La$^+$-C$_4$H$_6$ stretching and C-H bending frequencies of the corresponding ions are also determined, and the vibrational assignments are confirmed with deuterated ethylene measurements.