Vibrational spectra and molecular structure of sulfanilamide: IR and Low temperature Raman studies and DFT investigation of monomeric and dimeric forms

[Display omitted] •Low temperature Raman and room temperature Raman and IR spectra were experimentally investigated.•Computations of optimized geometries and related parameters were made for the lowest energy conformer and its dimer.•The low temperature Raman spectra show splitting of bands 1135 and 1590 & 1595 cm−1 indicating presence of dimer.•Vibrations involving S atom are under estimated while others are over estimated theoretically.•Five Quantum scaling factors are proposed for different regions. Raman spectra of sulfanilamide were recorded at temperatures 80, 90, 120, 150 and 300 K in the range 50-4000 cm−1. The room temperature FTIR spectrum of this compound was investigated in the range 400−4000 cm−1. The molecular structures and vibrational parameters for the lowest energy conformer of sulfanilamideand its dimer were carried out at the B3LYP/6−311++G** levelusing the Gaussian 09 software and PEDs have been calculated using the GAR2PED software. Low temperature Raman spectra enabled to observe some modes which were not resolved at room temperature.The low temperature Raman spectra show splitting of bands around 1135 and 1595 cm−1 which could be associated with the (C)NH2---SO2(NH2) interaction, which is indicative of the existence of sulfanilamide in dimeric form. Based on the present investigation five Quantum Scaling Factors (QSFs) are proposed.These QSFs provide better agreement between the observed and computed scaled frequencies.