A series of N
4X (X = O, S, Se) compounds have been examined with ab initio and density functional theory (DFT) methods. To our knowledge,
these compounds, except for the C
2v ring and the C
3v towerlike isomers of N
4O, are first reported here. The ring structures are the most energetically favored for N
4X (X = O and S) systems. For N
4Se, the cagelike structure is the most energetically favored. Several decomposition and isomerization pathways for the N
4X species have been investigated. The dissociation of C
2v ring N
4O and N
4S structures via ring breaking and the barrier height are only 1.1 and −0.2 kcal mol
−1 at the CCSD(T)/6-311+G*//MP2/6-311+G* level of theory. The dissociation of the cagelike N
4X species is at a cost of 12.1–16.2 kcal mol
−1. As for the towerlike and triangle bipyramidal isomers, their decomposition or isomerization barrier heights are all lower
than 10.0 kcal mol
−1. Although the C
S cagelike N
4S isomer has a moderate isomerization barrier (18.3–29.1 kcal mol
−1), the low dissociation barrier (−1.0 kcal mol
−1) indicates that it will disappear when going to the higher CCSD(T) level.
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