# Predicting the Initial Thermal Decomposition Path of Nitrobenzene Caused by Mode Vibration at Moderate-Low Temperatures: Temperature-Dependent Anti-Stokes Raman Spectra Experiments and First-Principals Calculations

journal contribution

posted on 02.10.2018, 00:00 by Yajing Peng, Xianming Xiu, Gangbei Zhu, Yanqiang YangThe lack of understanding of the
initial decomposition micromechanism
of energetic materials subjected to external stimulation has hindered
its safe storage, usage, and development. The initial thermal decomposition
path of nitrobenzene triggered by molecular thermal motion is investigated
using temperature-dependent anti-Stokes Raman spectra experiments
and first-principles calculations to clarify the initial thermal decomposition
micromechanism. The experiment shows that the symmetric nitro stretching,
antisymmetric nitro stretching, and phenyl ring stretching vibration
modes are active as increasing temperature below 500 K. The DFT method
is used to examine the effects of the three mode vibrations on the
initial decomposition of nitrobenzene by relaxed scan for each relevant
change in bond lengths and bond angles to obtain the optimal reaction
channel leading to initial thermal decomposition of nitrobenzene.
The results demonstrate that the initial thermal decomposition is
the isomerization of nitrobenzene to phenyl nitrite. The optimal reaction
channel leading to the initial isomerization is the increase or decrease
of angle O–N–C from the antisymmetric nitro stretching
vibration, which causes the torsion of nitro group and the subsequent
oxygen atom attacking carbon atom. The scanning energy barrier related
to angle O–N–C is about 62.1 kcal/mol, which is very
consistent with the calculated activation barrier of isomerization
of nitrobenzene. This proves the reliability of our conclusions.