Anomalous Change of Bond Energies in the Cluster Ion N2H+(H2)n

Abstract

Gas-phase clustering reactions N2H+(H2)n-1 + H2 = N2H+(H2)n with n = 1−13 were studied using a pulsed-electron beam mass spectrometer. Anomalous changes of binding energies in the cluster ion N2H+(H2)n were observed, i.e., the bond energies of N2H+(H2)n increase with n = 2 → 5. The molecular orbital (MO) calculation revealed that the charge transfer takes place in the cluster ion N2H+(H2)n from the H2 ligands to the N2H+ moiety, with increase of n leading to the self-tightening of the bonds in the cluster ions. The experimental bond energies of N2H+(H2)n (n = 2−7) were reproduced by the ab initio MO calculations. The larger cluster ions N2H+(H2)n (n = 10−13) were found to coexist with smaller ones with n = 6−9 in the temperature region of 65∼40 K. This suggests the presence of the structural isomers.