Knowledge Bank

Reactions of acetylene (C$2$H$2$) with laser-vaporized La atoms produced La(C$6$H$4$) and La (C$\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$H$8$) in supersonic molecular beams. The organic fragments in these complexes were benzyne and naphthalene. The benzyne species was produced by the La-mediated cyclotrimerization of three acetylene molecules, whereas naphthalene was formed likely by the cyclization of the transient benzyne with two additional acetylene molecules. These cyclized products were identified by mass-analyzed threshold ionization mass spectroscopy, which measured adiabatic ionization energies and several vibrational frequencies. The measured ionization energies were 40875 (5) cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ for La(C$6$H$4$) and 36767 (5) cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ for La(C$\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$H$8$). The most active vibrational transitions of both complexes were metal-ligand stretching with 326 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ for La(C$6$H$4$) and 286 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ for La (C$\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$H$8$). By combining the spectra with theoretical calculations, the ground electronic states of the neutral complexes were determined to be $2$A$1$ (C) and $2$A (C) and those of the corresponding ions were $1$A$1$ (C) and $1$A (C) for La (C$6$H$4$) and La(C$\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$H$8$), respectively.