Harmonic and anharmonic analysis of the IR and Raman spectrum of macrocyclic dioxopolyamine

• Vibrational spectrum was analyzed in harmonic and anharmonic approximations.
• Anharmonic correction shows a better performance on prediction of CH modes.
• Large errors mainly origin from intermolecular hydrogen bonds.

A detailed analysis of the vibrational spectra of 8,8a,9,10,11,12,12a,13-octahydrodibenzo[b,h][1,4,7,10] dioxadiazacyclododecine-7,14 (6H,15H)-dione has been conducted in harmonic and anharmonic approximation. B3LYP and B3LYP-D3 functionals and 6-31G(d), 6-31+G(d,p) and TZVP basis set were employed. The calculated frequencies were compared with experimental fundamentals and the error distribution was analysis by Root Mean Square Deviation (RMSD). When a relatively large basis set (6-31+G(d,p)) is adopted, anharmonic approximation presents a overall advantage than empirical scaling factor method, when a medium basis set (6-31G(d)) is adopted, empirical scaling factor method provides a better accuracy than anharmonic approximation, except for ν(CH2) and ν(CH) mode. Anharmonic approximation cannot reduce the large errors of ν(NH), δ(NH) and ν(CO) modes. The bimolecular model reveals that these errors mainly arise from intermolecular hydrogen bonds. Van der Waals correction on DFT makes a significant improvement on prediction of ν(CH2) and ν(CH) modes but a negligible change on the other modes.

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