Ab initio calculations on Al2N4 and AlNn (n=4 to 7): potential precursors of high energy density materials

Lee, Edmond P.F., Dyke, John M. and Claridge, Rob P. (2002) Ab initio calculations on Al2N4 and AlNn (n=4 to 7): potential precursors of high energy density materials. Journal of Physical Chemistry A, 106 (37), 8680-8695. (doi:10.1021/jp021059q).

Abstract

Geometry optimization and harmonic vibrational frequency calculations have been carried out on various structures and low-lying, high- and low-spin electronic states of Al2N4 and AlNn clusters, where n = 4 to 7, at the B3LYP, MP2, and QCISD levels. The aim of these calculations was to search for states/structures that may be suitable candidates as precursors of high energy density materials. Well-bound charge-transfer states/structures with activated NN bonds were obtained. The exothermicities of the decomposition reactions of these states/structures to N2 molecules were computed at up to the RCCSD(T)/aug-cc-pVQZ(no g) level of theory. The most exothermic decomposition reaction considered is AlN6 Cs Al·NN2N2N (N6 ring), 4A' ', (a')1(a')1(a' ')1?Al + 3N2. The calculated ?H298 K is -226 kcal/mol, giving an energy release of over 75 kcal/mol per N2 molecule. We conclude that AlNn systems are potential precursors of high energy density materials. In addition, the HOMOs of these states/structures have been examined in order to understand the stability of these states/structures. The ability of aluminum to introduce various degrees of covalency and ionicity to such clusters, which will stabilize the polynitrogen system, has been discussed.

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Contributors

Author: John M. Dyke

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