Photodissociation dynamics of dinitrite at 355 nm: initiation of a reactive pathway

Direct observation of the intermediate radical in the photodissociation of 1,3-cyclohexane dinitrite

A two-step photodissociation mechanism was proposed in the literature for dinitrites in the absence of direct evidence of the intermediate species. In this work, photodissociation dynamics of cis and trans 1,3-cyclohexane dinitrites are investigated by laser-induced fluorescence (LIF) spectroscopy and theoretical calculation methods. Observation of the fluorescence spectra of the 3-nitrosooxy cyclohexoxy radical provides direct experimental evidence that the intermediate species exists. The results indicate that photodissociation of dinitrites indeed follows a two-step mechanism, i.e. one of the O-NO bonds of the molecule breaks first upon 355 nm laser photolysis and generates an alkoxy radical (RO) plus NO; the alkoxy radical further dissociates in the secondary dissociation step and produces small fragments such as vinoxy etc.

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

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.