Molecular Structure, Vibrational, NBO, HOMO-LUMO Analysis, and First Order Hyperpolarizability of 1 -Fluoro-2-Nitrobenzene Molecule Using Density Functional Theory

Abstract
This study presents a comprehensive theoretical structural analysis of the 1-Fluoro-2 Nitrobenzene molecule (abbreviated as 1F2NB) utilizing Density Functional Theory (DFT) methodology. The investigation encompasses an in-depth examination of the molecular structure, harmonic vibrational frequencies, molecular properties, molecular electrostatic potential (MEP) mapping, HOMO-LUMO analysis, natural bond orbital (NBO) analysis, and nonlinear optical (NLO) properties of 1F2NB, in conjunction with experimental spectroscopic measurements. The vibrational frequencies, calculated at the B3LYP/6-311++G (d,p) level, are scaled using the empirically derived relationship νobs/νcalc = 1.0087-0.0000163(νcalc / cm-1). This scaling approach, in comparison to uniform scaling, demonstrates a superior capacity to predict vibrational wavenumbers with exceptional accuracy, facilitating refined band assignment and enabling a more precise simulation of FT-IR and FT-Raman Spectra. The DFT calculations employing the B3LYP/6-311++G** basis set exhibit remarkable concordance with experimental IR and Raman spectra, with computed geometrical parameters and fundamental frequencies closely aligning with the observed data.

Key words: Density Functional Theory, Optimized geometry, Wavenumber-linear scaling method Halonitrobenzenes, Vibrational frequencies.