FRONTIER-CONTROLLED STRUCTURES OF THE GAS-PHASE A-PLUS-OR-MINUS(CS2)(N) CLUSTERS, A-PLUS-OR-MINUS=S-2(+), CS2+, S-2(+), AND CS2-

The gas-phase equilibria of the clustering reactions of A(+/-)(CS2)(n-1) + CS2 = A(+/-)(CS2)(n), A(+/-) = S-2(+), CS2+, S-2(-), and CS2-, were studied with a pulsed electron-beam high-pressure mass spectrometer. The A(+/-)...CS2 bond dissociation energies are 30.9 (A(+) = S-2(+)), 24.9 (A(+) = CS2+), 19.1 (A(-) = S-2(-), and 21.9 kcal/mol (A(-) = CS2-). The A(+/-)(CS2)...CS2 bond dissociation energies are less than 9 kcal/mor. The rates for the formation of S-2(+)-(CS2), S-2(+)(CS2)(2), S-2(-)(CS2), and CS2-(CS2) are found to become slower with a decrease of the ion source temperature. This suggests the presence of energy barriers for the formation of these cluster ions. Through the ab initio geometry optimizations, the most stable cation-radical clusters are found to be of the one-site SS interaction and anion-radical ones are of the four-membered ring form. The ''bent'' van't Hoff plot for S-2(+)(CS2) + CS2 = S-2(+)(CS2)(2) corresponds to coexistence of two geometric isomers with a similar stability. The most stable structures of n = I clusters are found to be frontier-orbital controlled. Less stable n = 1 isomers are also found and are charge-controlled.