Figure 7.

a) A model of a CH₃ group with the tilt (θ), azimuthal (φ) and twist (ψ) angles defined. b) Measured values of the asymmetric stretch vibration of CH₃ for lysozyme adsorbed at hydrophilic silica surfaces from different bulk concentrations. The error of the ratios is about 20 %. c) ${\chi }_{\mathit{yyz}}^{(2)}/{\chi }_{\mathit{yzy}}^{(2)}$ ratios for the CH₃ (as) vs. θ, assuming isotropic φ and ψ. If the gaussian distribution function for θ is broad, the tilt angle sensitivity is low, illustrating the difficulty to specifically identify one angle for complex macromolecules. The data are reprinted from ref [101], copyright 2003 American Chemical Society.