Three Gemini cationic surfactants (GI-surfactants) of different hydrophobic chain lengths based on di-imine compound, abbreviated as GI-6, GI-12 and GI-14, were synthesized and characterized using FT-IR and 1 HNMR. The surface-active parameters calculated in acidic media were discussed. The inhibition performance of GI-surfactants for X65-steel corrosion was assessed by weight loss and electrochemical techniques in 1M HCl and was accompanied by surface analysis and theoretical studies. The resistance of X65-steel was enhanced to nearly ⁓764 ohm.cm 2 after adding 1x10 -3 M of GI-14. This inferred a protective film formation on the X65-steel surface via adsorption phenomena that followed the Langmuir isotherm. The GIsurfactants' inhibition efficiency exceeded 95% at room temperature and 93 % at 328 K owing to the electron-rich centers' presence in their chemical structures. The relation between the prepared GI-surfactants molecular structures and their corrosion inhibition performance was studied theoretically based on DFT and MCs methods. The safeguard effect of GI-surfactants was confirmed by SEM and EDX. The comparison study between the GI-surfactants' performance and the previously reported compounds confirmed their high potential applications as corrosion inhibitors.

The Raman (3500−100 cm -1 ) and mid-infrared (4000−400 cm -1 ) spectra in addition to the 1 H NMR chemical shifts (δ, ppm) of ((N 1 Z, N 4 E)-N 1 , N 4 -bis (4 (dimethylamino) benzylidene) butane 1,4-diamine) Schiff base (Molecular formula, C22H30N4) has been recorded. Moreover, we have carried out full geometry optimization followed by frequency calculations using the DFT-B3LYP method employing 6-31+G(d) basis set to include the polarization and diffusion functions. The Raman activities and infra intensities favour a slightly distorted symmetric molecule with an inversion center. Aided by the calculated wavenumbers assembled with Raman and infrared spectral observations, we have provided complete/reliable vibrational assignments for all fundamentals with the exception of those anticipated below 100 and 400 cm -1 , respectively, this is true regardless of whether or not any fundamentals were found either overlapped or coincident. Analyses of normal coordinates provide support for the prevailing spectral interpretations, that were based on the computed atomic displacements in x, y and z Cartesian coordinate (ADCC) from B3LYP/6-31+G(d). All results are reported herein and compared with similar molecules whenever appropriate.