Mechanism for unimolecular decomposition of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine) an ab initio study

Citation
D. Chakraborty et al., Mechanism for unimolecular decomposition of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine) an ab initio study, J PHYS CH A, 105(8), 2001, pp. 1302-1314
Citations number
46
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY A
ISSN journal
1089-5639 → ACNP
Volume
105
Issue
8
Year of publication
2001
Pages
1302 - 1314
Database
ISI
SICI code
1089-5639(20010301)105:8<1302:MFUDOH>2.0.ZU;2-4
Abstract
To improve the mechanistic understanding of the possible decomposition in t he gas phase of the energetic material HMX (octahydro-1,3,5,7-tetranitro-1, 3,5,7-tetrazocine), we used ab initio calculations to determine the various unimolecular decomposition channels. We find three distinct mechanisms: (i ) homolytic cleavage of N-N bond to form NO2 (M = 46) and HMR (M = 250) whi ch subsequently decomposes to form various products (ii) successive HONO el iminations to give four HONO (M = 47) plus a stable intermediate (M 108); ( iii) O-migration from one of the NO2 groups of HMX to neighboring C atom fo llowed by the decomposition of intermediate (M = 296) to INT222 (a ring-ope ned RDX structure) and MN-oring (M = 74), which can undergo dissociation to smaller mass fragments. The decomposition scheme for HMX is similar to tha t for RDX presented earlier (J. Phys. Chem. A 2000, 104, 2261), except that concerted decomposition of HMX to four MN (M = 74) molecules is not a favo rable decomposition pathway, whereas this pathway was found in RDX decompos ition (both experimentally and theoretically). The formation of RDR-o in th e N-N homolysis pathway 1 or the formation of INT222 in pathways 1 and 3 pr esents an unified mechanistic scheme for the decomposition of both of these nitramines. The HMX decomposition mechanism correlates with available cond ensed phase experimental results, but detailed comparison of the predicted gas phase energetics is not possible.