Ultrafast Processes in Energetic Molecules

Abstract

The thesis has been presented in two parts. In first part of the thesis, ultrafast relaxation dynamics of UV excitation induced chemistry via electronically excited states has been discussed. Taking one example from each functional group (nitro groups, such as -CNO2, -NNO2, and -ONO2), -N3 (azide group), -N=N- (diazo group), -N(O)=N- (azoxy group)) the nature of ultrafast relaxation dynamics of energetic molecules is discussed in separate chapter. The content of the thesis is presented in the following way. In chapter 2, detail theoretical background of ab initio multiple spawning (AIMS) has been presented. In chapter 3, comparison of ultrafast relaxation dynamics and mechanism of nitro-containing molecules, nitromethane (containing C–NO2 active moiety), dimethylnitramine (containing N–NO2 active moiety), and methyl nitrate (containing O–NO2 active moiety) from electronically excited state (S1) has been discussed using ab initio multiple spawning (AIMS) dynamics simulations. Comparison of relaxation dynamics of 1,2,4,5-tetrazine and 1,2,4,5-tetrazine-2,4-di-N-oxide has also been discussed. In chapter 4, ultrafast electronically nonadiabatic chemistry of methyl azide (CH3N3)8 as a model system of azide-based energetic plasticizer bis(1,3-diazido prop-2-yl)malonate has been explored by using AIMS simulation. In chapter 5, a comparison of two different internal conversion dynamics of azo and azoxy energetic moieties through the (S1/S0)CI conical intersection has been presented. In chapter 6, we have explored the role of dissociative (π,σ*) states of furazan and triazole energetic molecules in the ring opening mechanism. The second part of my thesis focuses on strong field ionization induced chemistry of energetic molecules. In chapter 7, As a generic consequence of the interaction of a strong laser field with molecules, high harmonic generation from the energetic molecule, nitromethane (CH3NO2) has been discussed. Observing HHG from energetic molecules has ultimately opened two new directions in the field of laser ignition chemistry. Experimentally observed HHG spectra have been compared with the theoretical simulated spectra using molecular electrostatic potential. In chapter 8, another direction which has opened as an initial step of strong field ionization of energetic molecules is attosecond charge migration between fuel oxidizer has been discussed. In this chapter attosecond chemical bonding and its consequences in the initial step of laser ignition chemistry has been discussed for ethylene-O2, benzene-O2, methanol-O2 van der Waals complexes. Finally, in chapter 9, general conclusions, unfinished works, and future directions has been presented.