Figure 3.

Tilt-angle dependence of the χ_zzz/χ_xxz ratio for a single amide-I residue, for (a) the ψ-averaged case and two fixed-ψ cases (ψ=0 corresponds to the C(O)N bond lying in the yz plane) and (b) the ψ-averaged case for Gaussian distributions of tilt angles with different full-width-at-half- maxima (indicated). In (a) and (b), the tilt angle θ is defined as the angle between the transition dipole and the surface normal.