Table 1.

Assignation of vibrations from the Raman spectrum of food dye indigo carmine, standard indigo carmine, and the calculated Raman spectrum for and vibrations found in Facio and comparison with literature data.

Food Dye	INDIGO Carmine Exp.	Spectrum Calculated	Band Vibrations from Facio Obtained in This Work	Ref.
Spectrum	Spectrum
Raman shift [1/cm]	Raman shift [1/cm]
549	552	561	C-C ring bending: weak; C-H bending: weak; N-H bending: weak; S-O bending: weak	[42,48,49]
676	674	669	C-C ring bending: weak; C-H bending: weak; N-H bending: weak	[31,48,49]
723	723	705	N-H bending: medium; C-H bending: medium; S-C stretching: weak	[49]
766	766	761	C-C ring stretching: weak; C-H bending: weak	[42,48,49,50,51,52,53]
869	864	856	C-C-C ring bending: weak; C-N bending: weak	[42,49]
1040	1030	1052	C-H bending: strong; C-S stretching: medium; C-C ring stretching: weak	[42,48,49]
1137	1137	1157	C-H bending: strong; S-O stretching: weak	[48,49,53]
1183	1183	1157	C-C ring stretching: medium; C-H bending: strong; N-H bending: weak	[42,48,49,50,51,52]
1248	1240	1235	C-H bending: strong; N-C asymmetrical stretching: medium; C-C ring stretching: weak	[42,48,49,50,51,52,53]
1294	1296	1293	C-H bending; C-C ring stretching; N-H stretching	[42,48,49,51,53]
1348	1346	1349	C3 = C4 stretching: strong; C-C ring stretching; C-N ring stretching; C-H bending	[42,48,51,52]
1442	1473	1458	C-C ring stretching; C-H bending: strong C13-H32, strong C24-H36; N-H bending: weak N5-H29, weak N18-H33	[42,48,49,50,52,53,54]
1578	1576	1588	C = C ring-ring stretching: strong C3-C4; C-C ring stretching; C = O stretching; N-H bending	[42,48,49,50,51,52,53,54,55,56]
1625	1626	1625	C = C ring-ring stretching: strong C3-C4; C-C ring stretching; C = O ring symmetrical stretching	[42,48,49,50,51,52,53]
1699	1697	1703	C = C ring-ring stretching: strong C3-C4; C = O ring symmetrical stretching: strong C2-O1, strong C8-O9	[42,48,49,50,51,52,53,54,55]