FT-IR, FT-Raman, ab initio and DFT studies, HOMO–LUMO and NBO analysis of 3-amino-5-mercapto-1,2,4-triazole

The molecular vibrations of 3-amino-5-mercapto-1,2,4-triazole (AMT) have been investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopies. A detailed vibrational spectral analysis has been carried out and assignments of the fundamental modes have been proposed on the basis of peak positions and relative frequencies, atomic charges, HOMO–LUMO energies and several thermodynamic properties in the ground state were calculated using ab initio Hartree–Fock (HF) and Density Functional Theory, (B3LYP) with 6-311G(d,p) and 6-311++G(d,p) basis sets. With the aid of scaling procedures, observed wave numbers in FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected range. The theoretical IR and Raman spectra have also been constructed. Natural Bond Orbital (NBO) study explains charge delocalization of the molecule.

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► FTIR and FT-Raman spectra of the 3-amino-5-mercapto-1,2,4-triazole have been studied.
► The optimized geometrical parameters are obtained from ab initio and DFT calculations.
► The close agreement has been observed between the experimental and scaled frequencies.
► The HOMO and LUMO energies have been calculated.
► Natural Bond Orbital (NBO) study explains charge delocalization of the molecule.