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Sub-500 fs electronically nonadiabatic chemical dynamics of energetic molecules from the S-1 excited state: Ab initio multiple spawning study

Ghosh, Jayanta and Gajapathy, Harshad and Konar, Arindam and Narasimhaiah, Gowrav M and Bhattacharya, Atanu (2017) Sub-500 fs electronically nonadiabatic chemical dynamics of energetic molecules from the S-1 excited state: Ab initio multiple spawning study. In: JOURNAL OF CHEMICAL PHYSICS, 147 (20).

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Official URL: http://dx.doi.org/10.1063/1.4996956

Abstract

Energetic materials store a large amount of chemical energy. Different ignition processes, including laser ignition and shock or compression wave, initiate the energy release process by first promoting energetic molecules to the electronically excited states. This is why a full understanding of initial steps of the chemical dynamics of energetic molecules from the excited electronic states is highly desirable. In general, conical intersection (CI), which is the crossing point of multidimensional electronic potential energy surfaces, is well established as a controlling factor in the initial steps of chemical dynamics of energetic molecules following their electronic excitations. In this article, we have presented different aspects of the ultrafast unimolecular relaxation dynamics of energetic molecules through CIs. For this task, we have employed ab initio multiple spawning (AIMS) simulation using the complete active space self-consistent field (CASSCF) electronic wavefunction and frozen Gaussian-based nuclear wavefunction. The AIMS simulation results collectively reveal that the ultrafast relaxation step of the best energetic molecules (which are known to exhibit very good detonation properties) is completed in less than 500 fs. Many, however, exhibit sub-50 fs dynamics. For example, nitro-containing molecules (including C-NO2, N-NO2, and O-NO2 active moieties) relax back to the ground state in approximately 40 fs through similar (S-1/S-0) CI conical intersections. The N-3-based energetic molecule undergoes the N-2 elimination process in 40 fs through the (S-1/S-0) CI conical intersection. Nitramine-Fe complexes exhibit sub-50 fs Fe-O and N-O bond dissociation through the respective (S-1/S-0) CI conical intersection. On the other hand, tetrazine-N-oxides, which are known to exhibit better detonation properties than tetrazines, undergo internal conversion in a 400-fs time scale, while the relaxation time of tetrazine is very long (about 100 ns). Many other characteristics of sub-500 fs nonadiabatic decay of energetic molecules are discussed. In the end, many unresolved issues associated with the ultrafast nonadiabatic chemical dynamics of energetic molecules are presented. Published by AIP Publishing.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Depositing User: Id for Latest eprints
Date Deposited: 23 Dec 2017 06:14
Last Modified: 23 Dec 2017 06:14
URI: http://eprints.iisc.ac.in/id/eprint/58513

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