Multiple Isomers of La(C4H6) formed in reactions of La atom with small hydrocarbons

\chem{La(C_4H_6)} was observed from the reactions of laser-vaporized La atom with propene (\chem{CH_2CHCH_3}),isobutene [\chem{CH_2C(CH_3)2}],1-butyne (\chem{CHCC_2H_5}), and 2-butyne (\chem{CH_3CCCH_3}) in a metal cluster beam source and investigated by mass-analyzed threshold ionization (MATI) spectroscopy in combination with quantum chemical calculations and spectral simulations. La(cyclobutene) [La(\chem{CH_2CHCHCH_2})] and La(trimethylenemethane) [\chem{LaC(CH_2)_3}] were identified from the La + propene reaction. The formation of the two isomers involves two steps: the first step is the reaction of La+ \chem{CH_2CHCH_3} with the products of \chem{La(CH_2) + C_2H_4}, and the second step is the reaction of \chem{LaCH_2 + CH_2CHCH_3} which preduces \chem{La(C_4H_6) + H_2}. For the La + isobutene reaction, La(trimethylenemethane) was formed by dehydrogenation. For the reaction of La + 1- and 2-butynes, preliminary data analysis suggested that \chem{La(C_4H_6)} was formed by simple association. All these structural isomers have similar geometries in the neutral and singly charged ion states, as evidenced by the very strong origin bands and short Franck-Condon profiles in the MATI spectra