The C--H stretching region (2800---3200 cm -1) of the Raman spectrum of diptlrnitoyl phosphatidylcholine was resolved into 7
Lorentzian bands corresponding to CH 2 and CH 3 stretching ftmdamefltals and Fermi-resonance enhanced overtones and stimulated band profiles were compared with spectra recorded in L o, Po and L~ lamellar phases. Unlike all CH3 stretching vibrations which were conformation insensitive, the CH2 vibrations displayed decreasing spectral amplitudes/intensities except the partially allowed infrared active 2910cm -1 melting marker which gained intensity with progressing chain isomerization. The spectral change of the 2883 cm -1 band has two contributions: a linebroadening of the d~ antisymmetric CHz stretching fundamental (at constant intensity) which is a chain mobility effect, and an intensity decrease of the overlapping Fermi-resonance enhanced CH 2 bending overtone which is primarily a chain packing effect. Using vibrational and neutron diffraction data for the bilayer dimensions and with the assumption that the leading term in anharmonicity is the interchain interaction potential the intensity of the Fermi-resonance enhanced overtone was separated from that of the d~ antisymmetric CH2 stretching fundamental.