Anbu Veerappan* and Vijayalakshmi Karattadipalayam Arumugam Pages 5 - 21 ( 17 )
Density Functional Theory (DFT) computations have been proposed in this work to predict the spectroscopic characteristics and nonlinear optical properties of an energetic molecule N-Methyl-N-(2,4,6-trinitrophenyl) nitramide (MTNPN). FT-IR spectrum of MTNPN was recorded and the active modes were assigned. The normal modes were investigated with the help of normal coordinate analysis and force-field computations using DFT. The natural bond orbital analysis was performed to understand the intramolecular charge transfer interaction and the stability of the molecule. The first order hyperpolarizability of MTNPN was predicted in order to confirm its Non-Linear Optical (NLO) response and the results were compared with powder second harmonic generation experiment using Kurtz and Perry technique. The nucleophilic and electrophilic reactive sites have been obtained by the frontier molecular orbit and electrostatic potential surface.
Background: Earlier studies on the energetic molecule MTNPN show a small HOMOLUMO energy gap. In general, the material which acquires small energy gap exhibits NLO response and identical counterparts in both IR and Raman spectra. Hence, the combined experimental and theoretical studies were performed to explore the fundamental properties of the molecule.
Objective: The objective of this study was to explore the fundamental structural properties of an 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 vibrational normal modes and structural properties of the molecule. Kurtz and Perry technique is used to find second harmonic generation efficiency in comparison to the standard NLO reference material.
Results: The potential energy distribution was used to assign the vibrational normal modes of the molecule. The second order perturbation energies between the lone pair and antibonding species were predicted to understand the driving forces of molecular stability. The chemical reactivity of the molecule was determined from the molecular electrostatic potential surface and global reactivity descriptor results. The second-order hyperpolarizability of MTNPN and SHG efficiency of MTNPN were studied to find its NLO response and it was found from the results that MTNPN exhibits high NLO response than the standard NLO reference material. The vibrational degrees of freedom of MTNPN molecule were assigned and the experimental FT-IR spectra were compared with the scaled harmonic frequencies. The predicted second-order hyperpolarizability of MTNPN was about 6.46 times greater than the standard NLO reference urea. The interacting species between the lone pair orbitals and antibonding orbitals such as n3O8→ π*(N7-O9), n3O11→ π*(N10-O12) and n3O14→ π*(N13- O15) stabilized the molecule to a greater extent.
Chemical reactivity, DFT calculations, FT-IR spectrum, Kurtz Perry technique, N-methyl-N-(2, 4, 6-trinitrophenyl) nitramide, NLO properties, molecular electrostatic potential surface, second-order perturbation energies.
Research and Development Centre, Bharathiar University, Coimbatore, 641 046, Department of Physics, Sri Vasavi College, Erode, 638 316