W0342

Low-Temperature Dihydronium Ion Structure. J.R. Deschamps*, C. George, and A. Purdy, *Code 6030, Naval Research Laboratory, 4555 Overlook Ave., Washington, DC 20375, deschamps@nrl.navy.mil.

There are a number of reports of dihydronium ions in the solid state. The April 2002 release of the Cambridge Structural Database contains 36 occurrences in which the O...O separations are less than 2.6 Å between H₃O⁺ and H₂O pairs. The geometry of the dihydronium ion is of interest to modelers and theoreticians. Prior studies relied on geometrical constraints to refine the H-atoms. In the current study, the data quality is sufficient to refine all of the dihydronium H-atom positions. The strong hydrogen bond between the water molecules is nearly linear, with the O–H...O angle equal to 177(2)°. The central H atom in the cation has O–H distances of 1.15 (2) Å and 1.27 (2) Å. The dihydronium O atoms are pyramidal, with the O-atom 0.28(2) Å and 0.32(2) Å out of the plane formed by the three H-atoms surrounding each O-atom.