Abstract

European Journal of Mass Spectrometry
Volume 15 Issue 4, Pages 459–469 (2009)
doi: 10.1255/ejms.1008

Unimolecular and collision-induced dissociation of singly- charged mono-bromide silver clusters Ag_xBr⁺ (x = 2, 4, 6, 8, 10)

Hirofumi Nagao,^a,* Michisato Toyoda,^b Shigeo Hayakawa,^c Kenichi Iwamoto,^c Toshio Ichihara,^b Kazuya Kawamura^b and Kunio Awazu^a
aDivision of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. E-mail: nagao@mass.phys.sci.osaka-u.ac.jp
^bDepartment of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
^cDepartment of Chemistry, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuencho, Nakaku, Sakai, Osaka 599-8531, Japan

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.

Keywords: bromide silver cluster, spherical jellium model (SJM), unimolecular dissociation, collision-induced dissociation (CID), dissociation channel, thermochemical data

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