Knowledge Bank

The reactions of $Cl2$ and $F2$ with alkali metals to produce $M+X2-$ species in matrices have been studied by uv-visible, infrared, and Raman spectroscopy. The observed spectra correspond in each case to a species having an intraionic vibrational frequency about half that of the neutral halogen molecule. In this work, the mixed halogen ClF was reacted with alkali metals in argon matrices to produce the $M+ClF-$ species. Infrared spectra showed bands near $340cm-1$ assignable to the intraionic mode of $ClF-$ with $K+,Rb+$ and $Cs+$. In each case, the frequency was about midway between the corresponding bands for $F2-$ and $Cl2-$. The interionic mode was observed at $287cm-1$ with K, 241$cm-1$ with Rb, and $224cm-1$ with Cs. In addition, bands corresponding to appropriate salt molecules and trihalide anion species were observed in the infrared spectra. Bands corresponding to the intraionic mode were observed in Raman spectra at $338cm-1$ with Cs, and $340cm-l$ with Rb, using 4880 {\AA} exciting radiation. The $M+C12-$ species, as well as the $C12$ and ClF neutral molecules, were also observed in Raman spectra. Ultraviolet absorption experiments with Rb, Cs, and K showed two bands at 250 nm and 290 nm. The 250 nm band was favored slightly in experiments with high metal concentrations, and the 290 nm band was dominant with less metal. Photolysis with a low-pressure mercury are caused a substantial decrease in the intensity of the 290 nm band, and subsequent thermal cycling to 40$\circ K$ and 45$\circ K$ caused the 290 nm band to decrease further and the 250 nm band to grow in intensity. The 290 nm band in due to the $\sigma \to \sigma \ast$ transition of the $ClF-$ species. The 250 nm band is assignable to the secondary reaction products $M+ClF2-$ and $M+Cl2F-$ species.