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

Abstract

The 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.

Unimolecular Decomposition Reactions of Picric Acid and Its Methylated Derivatives─A DFT Study

“…Among the external stimuli challenging the stability of energetic materials is impact or shock. ,, The impact sensitivityone of the most common measures of sensitivityis usually determined by the drop hammer test, − where a hammer is dropped upon a sample of the material and the height at which an explosion is observed for some predetermined fixed percentage of the drops is recorded as the critical impact height. In the commonly employed Bruceton method, the critical impact height ( h 50 ) is defined as the distance from which 50% of the drops lead to explosion.…”

Phase transition and trigger mechanism of initial reaction under pressure for benzofuroxan energetic materials: Raman spectroscopy and first‐principle calculations

“…Without loss of generality, the proportion of the anti‐Stokes intensity over all modes is chosen to describe the energy proportion of the modes for simplification, which is expressed as [ 1 ] …”

“…The calculation results show that the activation modes II–VI are almost impossible to trigger chemical reactions (see Figure S5) because they could only cause the cleavage of C–H or C–C bonds whose dissociation energy is very high (about 100 kcal/mol). [ 1,52 ] However, the mode I (518 cm −1 ) involved in out‐of‐plane vibration of furoxan ring is predicted to cause an open loop reaction as shown in Figure 11. It shows the molecular potential energy as a function of dihedral angle O‐C‐N‐O.…”

“…The reactions of energetic materials can be triggered by heat, electricity, mechanical impact, shock wave, light, and so on. [ 1,2 ] These initiation ways can be classified into two mechanisms: one is thermal effect, and the other is pressure effect. For the thermal effect, the classical “hot spot” model [ 3 ] and molecular simulation methods are widely used to study the initial chemical reaction mechanism of energetic materials.…”

Aquaphotomics investigation of the state of water in oral liquid formulation of traditional Chinese medicine and its dynamics during temperature perturbation

“…The change in peak position of the three Gaussian fitted peaks of the sample under temperature perturbation was examined to understand the effect of temperature on the hydrogen bonding of different relative intensities according to the ref. 48.…”