We measured the amide I' band profile of the IR, isotropic Raman, anisotropic Raman, and Vibrational Circular Dichroism spectrum Of poly-L-proline in D2O. The band shapes were modeled by using an algorithm that exploits the delocalized character of the excited vibrational states [R. Schweitzer-Stenner, J. Phys. Chem. B. 108 (2004) 16965]. The band shapes could be quantitatively reproduced by invoking the polyproline II or 3(1)-helix conformation for all peptide residues. This corroborates the notion that the combined use of the above spectroscopies is an ideal tool to discriminate different conformations associated with the so-called random coil state of peptides. (c) 2005 Elsevier B.V. All rights reserved.