Unimolecular and Collision-Induced Dissociation of Singly-Charged Mono-Bromide Silver Clusters AgxBr+ (x = 2, 4, 6, 8, 10)

Abstract

Relative intensities of singly-charged mono-bromide silver clusters Ag xBr+ formed from sputtering of a pressed pellet of silver bromide were measured by mass spectrometry. The obtained results suggest that the Ag xBr+ clusters have a structural formula of the form Ag x–1+(AgBr). The relative stability of Ag x–1+(AgBr) was determined by the intrinsic stability of the remaining metallic portion of the cluster (Ag x–1+) as predicted by the spherical jellium model (SJM). Unimolecular and high-energy collision-induced dissociation (CID) spectra of Ag xBr+ ( x = 2, 4, 6, 8, 10) clusters were also measured. In all of the spectra, the most intense fragment peaks were assigned to the Ag x–1+ ions accompanying the loss of AgBr. The difference in the relative intensities of the Ag x–1+ peaks between unimolecular dissociation and CID spectra led us to conclude that the weakest bond in the excited cluster Ag xBr+* is the Ag x–1+–AgBr bond and the structure of Ag xBr+ is a metallic Ag x–1+ ion cluster adduct with AgBr. The primary fragments observed in the CID spectra were also explained by the stabilities of the generated ion products and neutral fragments, both having even delocalized valence electrons. The present results were consistently explained by SJM. The dissociation behavior of Ag2Br+ can be explained on the basis of the calculated thermochemical data.