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

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-CCl4 interface and for micellization.