Hydrogen Bonding, Electron Transfer and Orbital Interactions between RDX and Al3O3-: Forces governing the initial encounter

18 December 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

As the first step in energy transfer from oxide passivated metal nanoparticles/surface defects to an energetic molecule for the controlled dissociation of the latter, the nature of the weak interactions between RDX and Al3O3- isomers are studied as a model system by DFT method with PBE0 functional and different basis sets (TZVP, Def2-TZVPP, TZ2P). Different electron density (NCI, IGMH, QTAIM, IQA, EDA-NOCV) and charge analysis methods (Hirshfeld, Mulliken, Hirshfeld-I, NPA) reveal that partial charge-transfer from Al3O3- to RDX via the C-H···O (1.851-2.481Å, O(2p)-to-C-H(*) type) and the C-H···Al (2.836-2.871Å, Al(3p)-to-C-H(*) type) interactions are possible. Hirshfeld analysis predicts 6-25% transfer of the -1 charge to RDX while Hirshfeld-I, NPA, and Mulliken predict 7-22%, 2-7%, and 7-13% transfer, respectively. Al3O3- (HOMO)-RDX (LUMO+n, n=0-3) type interactions including the charge transfer via the (ON)O···Al (2.846-3.511Å) interactions are found to excite the Al3O3 (kite) anion. The binding energies are in the -10 to -31 kcal/mol range. Vertical detachment energies of the complexes are within 2.5-3.9 eV, higher than the bare Al3O3- isomers by 0.3-1.3 eV. Complexation weakens the RDX structure and reduces the C-H stretching frequencies by 10-350 cm-1. Modulations in the bond lengths in the Al3O3 isomers shift the frequencies in the 0-1300 cm-1 region. New intermolecular vibrations enrich the terahertz region of the IR spectra. Complexation is found to augment the resultant dipole moment from 2.7 (Al3O3- (rec)) and 8.6 (Al3O3- (kite)) to the 2.9-16.0 Debye range, signalling effects on the workfunction of the aluminum oxide surfaces upon binding.

Keywords

RDX
aluminum oxide
cluster
anion
DFT
electron transfer
surface defects

Supplementary materials

Title
Description
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Title
Hydrogen Bonding, Electron Transfer and Orbital Interactions between RDX and Al3O3- : Forces governing the initial encounter
Description
Structures, changes in ONO angles, NO bond lengths, CN bond lengths upon complexation, vibrational frequencies, Coulombic interactions and percent point charge based components, changes in the Hirshfeld charges on RDX and Al3O3- atoms upon complexation, vibrational frequencies, dipole moment vectors of complexes, orbital interaction diagrams for two complex isomers, bare Al3O3- normal mode vectors, change in frequency distributions.
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