  In the present study, dissociative electron attachment (DEA) measurements
with gas phase HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine,
$C_4H_8N_8O_8$, have been performed by means of a crossed electron-molecular
beam experiment. The most intense signals are observed at 46 and 176u and
assigned to $NO_{2}^{-}$ and $C_3H_6N_5O_{4}^{-}$, respectively. Anion
efficiency curves for 15 negatively charged fragments have been measured in the
electron energy region from about 0-20 eV with an energy resolution of ~0.7 eV.
Product anions are observed mainly in the low energy region, near 0 eV, arising
from surprisingly complex reactions associated with multiple bond cleavages and
structural and electronic rearrangement. The remarkable instability of HMX
towards electron attachment with virtually zero kinetic energy reflects the
highly explosive nature of this compound. Substantially different intensity
ratios of resonances for common fragment anions allow distinguishing the
nitroamines HMX and royal demolition explosive molecule (RDX) in negative ion
mass spectrometry based on free electron capture.
