Characterization of (NH3)(n=1-6)NH+ clusters produced by 252Cf fragments impact onto a NH3 condensed target.
This paper reports the first characterization of the (NH(3))(n)NH+ cluster series produced by a 252Cf fission fragments (FF) impact onto a NH(3) ice target. The (NH(3))(n=1-6)NH+ members of this series have been analyzed theoretically and experimentally. Their ion desorption yields show an exponential dependence of the cluster population on its mass, presenting a relative higher abundance at n = 5. The results of DFT/B3LYP calculations show that two main series of ammonium clusters may be formed. Both series follow a clear pattern: each additional NH(3) group makes a new hydrogen bond with one of the hydrogen atoms of the respective {NH(3)NH}+ and {NH(2)NH(2)}+ cores. The energy analysis (i.e., D-plot and stability analysis) shows that the calculated members of the (NH(3))(n-1){NH(2)NH(2)}+ series are more stable than those of the (NH(3))(n-1){NH(3)NH}+ series. The trend on the relative stability of the members of more stable series, (NH(3))(n-1){NH(2)NH(2)}+, shows excellent agreement with the experimental distribution of cluster abundances. In particular, the (NH(3))4{NH(2)NH(2)}+ structure is the most stable one, in agreement with the experiments.
Physics Department, Pontifícia Universidade Católica, Rua Marques de São Vicente 225, Rio de Janeiro 22542-900, Brazil.
Francisco Alberto
FA
Fernandez-Lima
Thiago Messias
TM
Cardozo
R M
RM
Rodriguez
Cassia Ribeiro
CR
Ponciano
Enio Frota
EF
da Silveira
Marco Antonio Chaer
MA
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