  Structural relaxation in the peptide model N-methylacetamide (NMA) is studied
experimentally by ultrafast optical Kerr-effect spectroscopy over the
normal-liquid temperature range and compared to the relaxation measured in
water at room temperature. It is seen that in both hydrogen-bonding liquids,
beta relaxation is present and in each case it is found that this can be
described by the Cole-Cole function. For NMA in this temperature range, the
alpha and beta relaxations are each found to have an Arrhenius temperature
dependence with indistinguishable activation energies. It is known that the
variations on the Debye function, including the Cole-Cole function, are
unphysical, and we introduce two general modifications: one allows for the
initial rise of the function, determined by the librational frequencies, and
the second allows the function to be terminated in the alpha relaxation.
