A neutron diffraction and computer modeling study of the interatomic structure of phosphoric acid

Wide angle neutron diffraction in combination with H/D substitution was use d to determine the inter- and intramolecular structure of 100% phosphoric a cid (H3PO4, PA). From radial distribution functions g(HH)(r), g(HX)(r), and g(XX)(r) (where X is either O or P) the hydrogen bonds were found to be ch aracterized by a very short O...H distance (1.54 Angstrom). Within a molecu le, the orientation of an OH group was found to be preferably in one of the three O-P-O planes. In the interpretation of the radial distribution funct ions, use was made of preliminary results of molecular dynamics simulations . Temperature effects on the structure of PA were only found in the hydroge n bond structure, which becomes somewhat less well defined when heating up from room temperature to 60 degrees C. Polyphosphates could not be detected , probably due to the small degree of polymerization. (C) 1999 American Ins titute of Physics. [S0021-9606(99)50904-5].