Knowledge Bank

A search for fluorescent transitions of UCl$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$ was undertaken using samples that were isolated in solid Ar at 15K. Pulsed laser excitation was examined using the harmonics from an Nd/YAG laser (266 and 355 nm) and a dye laser operating in the 447-481 nm range. Several absorption and emission band systems were observed, with the emission spectra spanning the entire visible range. Fluorescence decay lifetimes were found to be either fast (a few hundred ns) or slow (tens of microseconds). Analysis of the vibrational progressions indicated that the carrier of these band systems was UO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$Cl$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$, rather than UCl$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$. Although present as a minor contaminant the UO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$Cl$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ clearly has a much higher fluorescence quantum yield than UCl$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$. IR spectroscopy was used to confirm the presence of UO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$Cl$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ in the matrix (absorptions at 898 and 969 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$). Assignment of the electronic transitions of UO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$Cl$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ is discussed in terms of the electronic structure of the UO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$$\mathrm{<mrow\; data-mjx-texclass="ORD">2+</mrow>}$ sub-unit.