ABSTRACT

                      Quantum chemical calculations have been widely used to monitor reaction mechanisms, to study inhibition of the corrosion of metals. DFT is considered as a very useful technique to probe as well as to analyze the experimental data.

This study proposes a joint experimental and theoretical investigation of FTIR and vibrational characteristics of Triazoles (4-amino- 4H-1, 2, 4-triazole-3, 5-dimethanol(ATD ) and 3-amino-5-methylthio-1H-1,2,4-triazole(SAMT)) and also the theoretical determination of the optimized molecular geometries, HOMO–LUMO, Mulliken charges and NBO analysis using Density Functional Theory (DFT) method were conducted focusing on the corrosion inhibition efficiencies of ATD and SAMT.The room temperature Fourier transforms infrared spectra of the compounds-ATD and SAMT were measured using a JASCO FT/IR-4100 spectrometer.

In this study, the geometry of the compounds ATD and SAMT   were optimized with  DFT/B3LYP method using 6-31G (d,p) basis set. The molecular structural parameters ,the complete vibrational analysis, NBO analysis, HOMO and LUMO analysis and Mulliken population analysis of the compounds ATD and SAMT  were performed on the basis of DFT calculations at the B3LYP/6-31G(d,p) basis set. The molecular structural parameters were compared with the available XRD data for ATD and showed excellent agreement. The FT-IR spectral measurement has been made both for the ATD and SAMT. The consistency between the calculated and experimental FT-IR data indicates that the B3LYP/6-31G(d,p) method can generates reliable geometry and related properties for the compounds. The difference between the observed and scaled wave number values of most of the fundamentals is very small. The corrosion inhibition efficiency of the inhibitors and the values, EHOMO, ELUMO, ELUMO - EHOMO and ΔN of inhibitors were calculated by DFT method are correlated. DFT method shows that ATD has better inhibitive efficiency than SAMT towards aluminium at lower inhibitor concentrations.

Key words: DFT/B3LYP method, vibration analysis, NBO analysis, HOMO and LUMO analysis and Mulliken population analysis