Quantum Chemical Studies on the Spectroscopic, Electronic Structural and Nonlinear Properties of an Organic N-methyl-N-(2,4,6- trinitrophenyl) Nitramide Energetic Molecule

摘要

Density Functional Theory (DFT) computations have been proposed in thiswork to predict the spectroscopic characteristics and nonlinear optical properties of an energeticmolecule N-Methyl-N-(2,4,6-trinitrophenyl) nitramide (MTNPN). FT-IR spectrumof MTNPN was recorded and the active modes were assigned. The normal modes were investigatedwith the help of normal coordinate analysis and force-field computations usingDFT. The natural bond orbital analysis was performed to understand the intramolecularcharge transfer interaction and the stability of the molecule. The first order hyperpolarizabilityof MTNPN was predicted in order to confirm its Non-Linear Optical (NLO) responseand the results were compared with powder second harmonic generation experiment usingKurtz and Perry technique. The nucleophilic and electrophilic reactive sites have been obtainedby the frontier molecular orbit and electrostatic potential surface.Background: Earlier studies on the energetic molecule MTNPN show a small HOMOLUMOenergy gap. In general, the material which acquires small energy gap exhibits NLOresponse and identical counterparts in both IR and Raman spectra. Hence, the combinedexperimental and theoretical studies were performed to explore the fundamental propertiesof the molecule.Objective: The objective of this study was to explore the fundamental structural properties ofan energetic molecule MTNPN in addition to its application as a non-linear optical material.Method: FT-IR technique and quantum chemical methods were used to analyze the vibrationalnormal modes and structural properties of the molecule. Kurtz and Perry technique isused to find second harmonic generation efficiency in comparison to the standard NLOreference material.Results: The potential energy distribution was used to assign the vibrational normal modesof the molecule. The second order perturbation energies between the lone pair and antibondingspecies were predicted to understand the driving forces of molecular stability. Thechemical reactivity of the molecule was determined from the molecular electrostatic potentialsurface and global reactivity descriptor results. The second-order hyperpolarizability ofMTNPN and SHG efficiency of MTNPN were studied to find its NLO response and it wasfound from the results that MTNPN exhibits high NLO response than the standard NLOreference material.The vibrational degrees of freedom of MTNPN molecule were assigned and the experimentalFT-IR spectra were compared with the scaled harmonic frequencies. The predictedsecond-order hyperpolarizability of MTNPN was about 6.46 times greater than the standardNLO reference urea. The interacting species between the lone pair orbitals and antibondingorbitals such as n3O8→ π*(N7-O9), n3O11→ π*(N10-O12) and n3O14→ π*(N13-O15) stabilized the molecule to a greater extent.