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Group 6 metal–bis(mesitylene)sandwich complexes are produced by interactions between the laser-vaporizedmetal atoms and mesitylene vapor in a pulsed molecular beam source,identified by photoionization time-of-flight mass spectrometry, andstudied by pulsed-field ionization zero-electron kinetic energy spectroscopyand density functional theory calculations. Although transition metal–bis(arene)sandwich complexes may adopt eclipsed and staggered conformations,the group 6 metal–bis(mesitylene) complexes are determinedto be in the eclipsed form. In this form, rotational conformers withmethyl group dihedral angles of 0 and 60° are identified forthe Cr complex, whereas the 0° rotamer is observed for the Moand W species. The 0° rotamer is in a C2vsymmetry with the neutral ground stateof 1A1and the singly positive charged ion stateof 2A1. The 60° rotamer is in a Cisymmetry with the neutralground state of 1Agand the ion state of 2Ag. Partial conversion of the 60 to 0° rotameris observed from He to He/Ar supersonic expansion for Cr–bis(mesitylene).The unsuccessful observation of the 60° rotamer for the Mo andW complexes is the result of its complete conversion to the 0°rotamer in both He and He/Ar expansions. The adiabatic ionizationenergies of the 0° rotamers of the three complexes are in theorder of Cr–bis(mesitylene) < W–bis(mesitylene)

η2-Propadienylidenelanthanum[La(η2-CCCH2)] and deprotiolanthanacyclobutadiene[La(HCCCH)] of La(C3H2) are identified fromthe reaction mixture of neutral La atom activation of propyne in thegas phase. The two isomers are characterized with mass-analyzed thresholdionization spectroscopy combined with electronic structure calculationsand spectral simulations. La(η2-CCCH2)and La(HCCCH) are formed by concerted 1,3- and 3,3-dehydrogenation,respectively. Both isomers prefer a doublet ground state with a La6s-based unpaired electron, and La(η2-CCCH2) is slightly more stable than La(HCCCH). Ionization of the neutraldoublet state of either isomer produces a singlet ion state by removingthe La-based electron. The geometry change upon ionization resultsin the excitation of a symmetric metal–hydrocarbon stretchingmode in the ionic state, whereas thermal excitation leads to the observationof the same stretching mode in the neutral state. Although the Laatom is in a formal oxidation state of +2, the ionization energiesof these metal–hydrocarbon radicals are lower than that ofthe neutral La atom. Deuteration has a very small effect on the ionizationenergies of the two isomers and the metal–hydrocarbon stretchingmode of La(η2-CCCH2), but it reduces considerablythe metal–ligand stretching frequencies of La(HCCCH). [ABSTRACT FROM AUTHOR]

The copper−monomethylamine and −dimethylamine complexes were produced in a supersonic jet and examined using single-photon zero kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The adiabatic ionization potentials (I.P.) of the complexes and vibrational frequencies of the corresponding ions were measured from their ZEKE spectra. The equilibrium geometries, binding energies, and vibrational frequencies of the neutral and ionized complexes were obtained from MP2 and B3LYP calculations. The observed vibrational frequencies of the ionic complexes were well-reproduced by both calculations, whereas the Franck−Condon intensity patterns of the spectra were simulated better by MP2 than B3LYP. The observed I.P. and vibrational frequencies of the Cu−NHn(CH3)3-n (n = 0−3) complexes were compared, and methyl substitution effects on their ZEKE spectra were discussed. [ABSTRACT FROM AUTHOR]