Sentence:  However , any oxygen nonequivalence would shorten either the already extremely short **f interlayer distance of 2.55 <WSD>A</WSD> or the non hydrogen bonded **f interlayer interactions which are already quite short at 2.58 A . 
Meaning of the word marked with <WSD> tags:  a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation