title: Spectroscopic analysis and DFT calculations of a food additive carmoisine.
abstract: FT-IR and Raman techniques were employed for the vibrational characterization of the food additive Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and pi-electron delocalization. Predicted electronic absorption spectra from TD-DFT calculation have been analysed comparing with the UV-vis spectrum. The first hyperpolarizability of the molecule is calculated. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C-H ...O, improper, blue shifted hydrogen bonds have been analysed using natural bond orbital (NBO) analysis.
authors.affiliation: Center for Molecular and Biophysics Research, Department of Physics, Mar Ivanios College, Thiruvananthapuram, 695015 Kerala, India.
authors.forename: M
authors.initials: M
authors.lastname: Snehalatha
authors.forename: C
authors.initials: C
authors.lastname: Ravikumar
authors.forename: I
authors.initials: I
authors.lastname: Hubert Joe
authors.forename: N
authors.initials: N
authors.lastname: Sekar
authors.forename: V S
authors.initials: VS
authors.lastname: Jayakumar
mesh_terms: D000042:Absorption; D004355:Drug Stability; D005503:Food Additives / Q000032:analysis* / Q000737:chemistry; D006860:Hydrogen Bonding; D015394:Molecular Structure; D009282:Naphthalenesulfonates / Q000032:analysis* / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013057:Spectrum Analysis / Q000379:methods*; D013059:Spectrum Analysis, Raman / Q000379:methods; D014732:Vibration
chemical_list: D005503:Food Additives; D009282:Naphthalenesulfonates; C006671:azo rubin S