Resonance raman spectra and tautomeric structures of a surface-active azo dye, CI Acid Red 138, adsorbed at the aqueous solution–air interface

Abstract Raman spectra of Gibbs monolayers adsorbed from the aqueous solution to the solution–air interface were measured for the first time using resonance Raman technique against a surface-active azo dye, CI Acid Red 138 (AR138). The tautomeric structure change of AR138 from the azo form to the protonated hydrazone form occurred upon adsorption from a basic solution. This structural change was principally the same as those observed previously for the adsorption at the aqueous solution-CCl 4 interface and for micellization.