A. Structure of the Isomers drawn in Molden TCBD (Tetrachlorobutadiene) consists of a total of four carbon atoms, two hydrogen atoms, and four chlorine atoms. In their research, Gurka and Titas examined nine distinct isomers of TCBD, each characterized by different placements of hydrogen and chlorine atoms within the molecule. The molecular structures of these isomers are illustrated in Figure , which presents the specific arrangements of the atoms. To offer a clearer and more intuitive view of the molecular geometries, Figure provides ball-and-stick models of the TCBD isomers, which were created using the Molden/6.2 visualization software. The Z-matrix representations of these isomers, detailing their precise atomic coordinates, are available in the supplementary section titled "Additional Data." In addition to the structural representations, Figure highlights the infrared (IR) spectra of the nine TCBD isomers, computed using Density Functional Theory (DFT) with the B3LYP and B3LYP-D3BJ functionals. A particular focus is given to isomer a, identified as the (E,E)-1,2,3,4-TCBD isomer, which is located in the top-left corner of the IR plot. Several key IR features are observed for this isomer. A significant peak is detected around 801 cm⁻¹, representing the C-Cl stretching motion, a characteristic vibration of chlorobutadienes . Additionally, a medium-intensity peak at 832 cm⁻¹ corresponds to the C=C bending mode, a fundamental vibration in chlorobutadiene compounds. Further notable peaks include a mediumintensity signal at 860 cm⁻¹, indicative of the C-H bending motion. Moving to higher wavenumbers, a medium peak at 1586 cm⁻¹ represents the C=C stretching vibrations, which are commonly observed in alkenes. Lastly, at 3252 cm⁻¹, a medium-intensity peak is visible, signaling the C-H stretching motion in the alkene moiety of the molecule. This comprehensive vibrational analysis provides detailed insights into the structural and bonding characteristics of the TCBD isomers, with each peak in the IR spectrum corresponding to specific molecular vibrations. The corresponding numerical data for the IR intensities and wavenumbers are available in the "Additional Data" section, offering further reference for detailed examination. Through the use of DFT methods, particularly B3LYP and B3LYP-D3BJ, the researchers were able to accurately model the molecular vibrations of the TCBD isomers, thus enhancing the understanding of their chemical structures and interactions. Similar peaks were observed for molecule B, suggesting its classification as an alkene due to the presence of characteristic C=C stretching vibrations. In addition to this, the bending of the halo compound's C-Cl bond was detected, alongside the bending and stretching of the C-H bond. These vibrational modes, which indicate both halogen and hydrocarbon bond motions, were consistent across the remaining TCBD isomers, ranging from TCBDc to TCBDi. The recurrence of these patterns reinforces the similarity in molecular structure among the isomers, particularly with regard to their alkene characteristics and halogen interactions. A detailed breakdown of the infrared (IR) spectroscopy absorptions for these isomers, arranged by specific frequency regions, is provided in Table . This table organizes the observed peaks and correlates them with their respective vibrational modes, offering a comprehensive view of the molecular dynamics in the TCBD isomers. The absorption regions cover a range of motions including stretching and bending vibrations of C=C, C-H, and C-Cl bonds, highlighting key features of alkene and halogen-containing molecules. Table complements this analysis by presenting the IR spectra values generated through Density Functional Theory (DFT) for each of the observed peaks. These values are categorized based on their relative strength, with peaks classified as strong (s), medium (m), or weak (w), depending on their intensity. The strongest peaks are associated with the maximum absorption values, which typically signify the most prominent vibrational modes in the molecular structure. This categorization allows for an easier comparison of vibrational intensities across different isomers, providing insights into the relative significance of various bond motions within each molecule. The detailed data from Tables and offer a valuable resource for interpreting the IR spectra and understanding the molecular structures of the TCBD isomers.