Molecular Structures of Perchloric Acid and Halogen Perchlorates ClOClO3 and FOClO3

The torsion–rotation spectrum of perchloric acid, HClO4

“…Although one can change the sign of D ab by adjusting the tilt or distortion of the ClO 3 group, it has already been noted that the behavior of the coefficient of P a P b + P b P a as a function of K cannot be ascribed to that of an inverse inertial tensor component for a particular structure. Although D ab is not readily obtainable from available structural data, the value of B À C as well as the change of B + C on isotopic substitution are consistent with what is expected on the basis of published theoretical and electron diffraction structures [7][8][9][10][11]. The change in B + C gives 10.9 pm for the Cl a coordinate.…”

“…Calculation of D ab from ab initio structures is also difficult since the sign and magnitude of the term depend strongly on the HOCl angle as well as the tilt and distortion of the ClO 3 group. However, both the experimental results [11] and the previously cited ab initio calculations place an upper limit of %30 MHz on |D ab |.…”

“…This can be compared with A 0 = 5609.76(13) MHz [37] for FClO 3 . Since both ab initio [7][8][9][10] and electron diffraction results [11] show that the ClO 3 group is slightly distorted, the close agreement may be fortuitous. The relationship…”

“…Several ab initio calculations have been performed to characterize HClO 4 , its other possible isomers, and clusters [7][8][9][10]. Casper et al [11] published an electron diffraction and ab initio study which utilized preliminary rotational constants from this work to aid in the structure determination. A projection of the molecule in the ab plane using structural parameters from that work is shown in Fig.…”

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“…The structures of XOClO 3 molecules have been investigated by electron diffraction in the gas phase. In all cases the longest bond for XO‐ClO 3 (X=H, F, Cl) amounts 164, 170, 171 pm, respectively160 and the related bond energies are estimated to be 250, 181 and 150 kJ mol −1 , respectively 161, 162. Therefore, the best precursor for the ClO 3 radical should be ClO‐ClO 3 .…”