EFFECT OF LATTICE ENERGY MISMATCH ON THE RELATIVE MASS PEAK INTENSITIES OF MIXED-ALKALI HALIDE NANOCRYSTALS

The relative mass peak intensity distribution of the [M(14-n)A(n)I(13) ](+) mixed alkali halide nanocrystals containing a ''magic'' number of 14 metal cations (M and A) and 13 iodide anions is examined. These na nocrystals were generated through sputtering of mixed solid alkali hal ides using fast atom bombardment and analyzed by use of a double-focus ing sector field mass spectrometer. The mass peak intensities of mixed cluster ions composed of two different metals relative to the ''pun'' nanocrystals (containing one or the other metal) are compared for two types of mixed cluster ions: one with small lattice energy mismatch, i.e., [Rb14-nKnI13](+) cluster ions, and the other type with large lat tice energy mismatch, i.e., [Cs(14-n)A(n)I(13)](+) cluster ions where A is either Na, K, or Rb. In contrast to what was previously(1) found for clusters with small energy mismatch in which the rate of formation (which depends on the possible number of isomers that each mixed clus ter ion can have) determines the relative intensities of mass peaks, t he rate of evaporation (i.e., the cluster instability) determines the relative mass peak intensities in salts with relatively large lattice energy mismatch. These results are consistent with our previously prop osed kinetic model for the formation and decay of these clusters.