title: Reactivity of aluminum cluster anions with ammonia: selective etching of Al11(-) and Al12(-).
abstract: Reactivity of aluminum cluster anions toward ammonia was studied via mass spectrometry. Highly selective etching of Al(11)(-) and Al(12)(-) was observed at low concentrations of ammonia. However, at sufficiently high concentrations of ammonia, all other sizes of aluminum cluster anions, except for Al(13)(-), were also observed to deplete. The disappearance of Al(11)(-) and Al(12)(-) was accompanied by concurrent production of Al(11)NH(3)(-) and Al(12)NH(3)(-) species, respectively. Theoretical simulations of the photoelectron spectrum of Al(11)NH(3)(-) showed conclusively that its ammonia moiety is chemisorbed without dissociation, although in the case of Al(12)NH(3)(-), dissociation of the ammonia moiety could not be excluded. Moreover, since differences in calculated Al(n)(-) + NH(3) (n=9-12) reaction energies were not able to explain the observed selective etching of Al(11)(-) and Al(12)(-), we concluded that thermodynamics plays only a minor role in determining the observed reactivity pattern, and that kinetics is the more influential factor. In particular, the conversion from the physisorbed Al(n)(-)(NH(3)) to chemisorbed Al(n)NH(3)(-) species is proposed as the likely rate-limiting step.
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Andrej
authors.initials: A
authors.lastname: Grubisic
authors.forename: Xiang
authors.initials: X
authors.lastname: Li
authors.forename: Gerd
authors.initials: G
authors.lastname: Gantefoer
authors.forename: Kit H
authors.initials: KH
authors.lastname: Bowen
authors.forename: Hansgeorg
authors.initials: H
authors.lastname: Schnöckel
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Tenorio
authors.forename: Ana
authors.initials: A
authors.lastname: Martinez