Knowledge Bank

Mixed solvent cluster ions were generated in our solvated alkali ion source by coexpansion of acetone and methanol seeded in argon. Control of the solvent concentration allowed clusters of various composition to be produced. A beam rich in acetone but lean in methanol yielded large amounts of $Cs+((CH3)2CO)N(CH3OH)M$ with $N=1$ to 12 and $M=1$ or 2. Pure $Cs+((CH3)2CO)N$ clusters do not absorb in the $CO2$ laser range. $Cs+(CH3OH)N$ clusters do absorb here, however, and have been well characterized. Single photon excitation of the methanol chromophore(s) in the mixed cluster ions was sufficient to predissociate the cluster. Comparison of the spectra with those of pure cesium-methanol clusters allowed us to probe methanol position within the mixed cluster ion. In this way the competitive binding of acelone and methanol to the cesium ion can be observed. Data for $N=3$ to 12, $M=1$ suggested that the ion was preferentially solvated by acetone and that four acetone molecules were necessary to displace a methanol molecule from the first solvent shell. Methanol molecules were displaced further from the ion as N increased above four. When two methanol molecules were present in the cluster, they occupied spectroscopically distinct sites.