What the stretch frequency spectrum of D2O/Ru(0 0 0 1) does and does not mean

Based on O–D stretch frequencies, Denzler et al., reject partial dissociation of D2O molecules as the explanation of the measured structure of 3×3 – D2O/Ru(0 0 0 1). But it is largely the O–O distance that determines the O–D stretch frequency in an O–D⋯O bond of an H-bonded network. Thus, a D2O adlayerʹs stretch spectrum reflects its O–O distances, not its proportion of intact vs. dissociated molecules. This idea suggests that deuteron disorder in the heavy-water adlayer is the key to understanding its broad O–D stretch spectrum.