Peter, if it's a covalently-bonded H atom it surely can't be a bare proton, it must have at least some partial electron around it for the (possibly partial) covalent bond, enough to diffract X-rays anyway. As you say the proton itself is invisible to X-rays.
Cheers -- Ian On 2 February 2015 at 13:08, Peter Moody <pcem1bigfi...@gmail.com> wrote: > Dear BB > > > I have (again) realised how limited by understanding of our subject is. > > > In Nature’s online site > http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14110.html?WT.ec_id=NATURE-20150129 > there is a paper describing an X-ray structure determined with sub-atomic > data (nice!). The figures show density for H+ as well as H-. In my > simple way I had assumed that any X-ray scattering from the nucleus was > negligible, and that the electrons are responsible for this. I would expect > a proton (i.e. H+) alone to be invisible to X-rays, and certainly not to > look similar to a hydride (with two electrons in (electron density) maps. > What have I missed? Could someone please explain, or point me to a > suitable reference? > > > Best wishes, Peter > > (please use peter.mo...@le.ac.uk to reply directly) > > http://www2.le.ac.uk/departments/biochemistry/staff/moody > >
