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Abstract

Ion bombardment of pure water ice by Au+ monoatomic and Aumath image and Cmath image polyatomic projectiles results in the emission of two series of water cluster ions—(H2O)math image and (H2O)nH+—with n ranging from 1 to >40. The cluster ion yields are very significantly higher under polyatomic ion bombardment than when using an Au+ primary ion. The yield of the protonated water species (H2O)nH+ is found to be enhanced by increasing ion fluence. Cmath image bombardment results in a very dramatic increase in the (H2O)nH+ yield and decrease in the yield of (H2O)math image. Aumath image also significantly increased the yield of protonated species relative to the non-protonated but to a lesser extent than Cmath image. Bombardment by Au+ also increased the yield of protonated species but to a very much smaller extent. The hypothesis that the protonated species may enhance the yield of [M+H]+ from solute molecules in solution has been investigated using two amino acids, alanine and arginine, and a nucleic base, adenine. The data suggest that the protons produced by the sputtering of water ice are depleted in the presence of these solutes and concurrently the yields of solute-related [M+H]+ and immonium secondary ions are greatly enhanced. These yield enhancements are analysed in the light of other possible contributors such as increased rates of sputtering under polyatomic beams and increased secondary ion yields as a consequence of solute dispersion. It is concluded that enhanced proton attachment is occurring in polyatomic sputtered frozen aqueous solutions. Copyright © 2006 John Wiley & Sons, Ltd.