Table 3 Assignments of the main selected vibrational modes of ETH (IR_Exp. – experimental IR band positions and R_exp. Experimental Raman band positions). The calculated data were obtained under vacuum, chloroform, methanol, and water using the DFT functional ωb97xd/6-311 + + g(d, p).

From: Experimental and computational analyses for elucidation of structural, electronic, thermal, and vibrational properties of ethionamide crystal

ω_Cal. [cm^− 1]						Assignments
Vacuum	Chloroform	Methanol	Water	IR_Exp.	R_Exp.	Assignments
288	297	296	296	–	274	τ(ring) + wag(N3H13H14)
364	361	358	358	–	329	δ(ring) + wag(N3H13H14)
442	440	442	442	441	–	δ(ring) + wag(N3H13H14)
483	459	483	487	461	–	δ(ring) + wag(N3H13H14)
526	523	526	526	525	531	δ(ring) + δ(C10H19H20H21) + ρ(C9H17H18) + tw(N3H13H14)
569	568	569	568	564	567	δ(ring) + δ(C10H19H20H21) + ρ(C9H17H18)
645	643	645	646	651	660	ρ(C9H17H18) + δ(C4C11S1N3) + δ(ring)
700	701	700	701	701	–	δ(ring) + ν(C11S1)
726	726	726	722	716	710	δ(ring) + ρ(C9H17H18) + δ(C10H19H20H21)
768	768	768	769	737	731	ν(ring) + δ(C10H19H20H21) + ρ(C9H13H18)
805	808	805	804	806	811	ν(ring) + δ(C10H19H20H21) + δ(C9C7H18H17) + ρ(N3H14H15) + ν(C11S1)
889	895	889	890	871	881	tw(C9H17H18) + ν(C8H16) + δ(C10H19H20H21)
978	979	979	979	980	995	br(ring) + δ(C10H19H20H21) + wag(C9H17H18) + ρ(N3H14H15)
987	988	987	987	998	–	ν(ring) + δ(C10H19H20H21) + wag(C9H17H18) + ρ(N3H14H15)
1044	1044	1044	1045	1051	1058	ν(ring) + δ(C10H19H20H21) + δ(C9C7H18H17)
1099	1098	1099	1099	1100	1105	ν(ring) + δ(C10H19H20H21)
1122	1121	1122	1124	1146	1152	ρ(N3H14H15) + ν(ring)
1199	1200	1200	1199	1200	1212	wag(C9H17H18) + ν(ring) + ρ(N3H14H15)
1247	1247	1246	1247	1254	–	tw(C9H17H18) + δ(C10H19H20H21)
1286	1289	1286	1285	1285	1293	ρ(N3H14H15) + ν(C11N3) + ν(ring)
1387	1388	1379	1380	1389	1398	sc(N3H14H15) + ν(C11N3) + ν(ring)
1412	1415	1411	1412	1414	1426	sc(C9H17H18) + ν(ring)
1472	1471	1472	1472	1472	1469	sc(C10H21H20) + sc(C10H19H21)
1570	1570	1569	1569	1552		sc(N3H14H15) + ν(ring)
1588	1588	1587	1588	1588	1596	sc(N3H14H15) + ν(ring)
1607	1606	1607	1607	1653	–	ν(ring)
2930	2929	2930	2930	2907	2902	ν_s(C10H20H21) + ν_s(C10H219H21) + ν_s(C10H20H29)
2970	2970	2970	2971	2963	2964	ν_s(C9H17H18)
3108	3107	3108	3108	3161	–	ν(C6H15) + ν(C5H12)
3461	3465	3461	3460	3472	–	ν_s(N3H14H15)
3583	3588	3582	3582	3608	–	ν_as(N3H14H15)

*τ, torsion; ω, wagging; sc, scissoring; ν, stretching; ν_a, anti-symmetric stretching; ν_s, symmetric stretching; δ, bending; tw, twisting; wag, wagging; ρ, rocking. br, breathing.
**Scaled frequencies (0.957×) improve agreement with experimental data. Modes involving C = S (e.g., 701 cm^− 1) show larger deviations due to crystal packing effects.

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Table 3 Assignments of the main selected vibrational modes of ETH (IR_Exp. – experimental IR band positions and R_exp. Experimental Raman band positions). The calculated data were obtained under vacuum, chloroform, methanol, and water using the DFT functional ωb97xd/6-311 + + g(d, p).

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