The Structure and Harmonic Frequencies

Dimensions of the unit cell (which contains four formula units of HC104-2H20) and positions of the heavy atoms were taken from Ref. [103]. Optimization of all atomic positions yields a stmcture with four equivalent H502 C104 units. In accord with the experimental data, the CPMD results suggest a structure in which the proton of the perchloric acid has been transferred to water and is shared by 

It should be noted that the X-ray study [103] considered the non-centrosymmetric PnliU structure as a possible choice, but the centrosymmetric space group Pnma was accepted as most suitable. We find that the latter corresponds to a transition structure with one imaginary frequency ( 7Si cm i). The transition 

The computed distances of different H-bonds in the crystal agree fairly well with the experimental values. The 0---0 distance in H5O2+ is 2.426 A (2.424 A) and H-bonds between the H5O2+ and C104 ions vary from 2.72 to 2.78 A (2.784, 2.788 A). Experimental values [103] are given in parenthesis. 

The harmonic frequencies of the isolated H5O2+ ion and the H5O2+ ion in the H502+C104 crystal are given for the region above 1000 cm in Table 9.2. (The four fundamentals of the CIO4- anion and their multiple components are located 

1) The symmetry of the H502 ion in the Pnma structure depends on the accuracy of the symmetrization procedure, s. 

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