The Heat of Formation of Xenon Tetroxide¹

Abstract

an efficient proton scavenger.11 Our data indicate that a trace of NH3 (1.5 mole %) completely stops the disappearance of CD4. This effect is similar to that of Xe in the radiation-induced H2-D2 exchange.2 Preliminary experiments indicate that Xe is not effective as a proton scavenger in the CH4-D2 system. Findings to date indicate that proton-transfer efficiencies may be ranked in the order NH3 > CH4 > Xe > D2, and that this order may be the same as that for the proton affinities of these molecules. Judicious use of NH3 to block ionic reactions in the D2-TD-CH4 system may permit accurate evaluation of the temperature coefficient for the atomic exchange reaction. Work directed toward establishment of a more inclusive scale of relative protontransfer efficiencies and toward elucidation of the atomic and free-radical exchange mechanism for CH4 and D2 is in progress.12

Calculations for XeOn (n = 2−4): Could the Xenon Dioxide Molecule Exist?

“…The main results of the calculations are presented in Tables 2 and 3 The heats of formation posed a greater challenge and eventually turned out to be the main reason for choosing the particular basis set used. The reported experimental values 16,17 are for solid XeO 3 and XeO 4 , while the calculations are performed for isolated molecules (gas phase). The enthalpy of sublimation of XeO 3 is estimated by Gunn 17 at 126(42) kJ/mol.…”

“…The reported experimental values 16,17 are for solid XeO 3 and XeO 4 , while the calculations are performed for isolated molecules (gas phase). The enthalpy of sublimation of XeO 3 is estimated by Gunn 17 at 126(42) kJ/mol. No energy of sublimation of XeO 4 was available to us; thus we estimated a value of 42 kJ/mol (10 kcal/mol) by analogy with other similar compounds, notably the likewise tetrahedral, "heavy" OsO 4 .…”

Spontaneous Dissociation of Xenon Tetroxide: Phase and Structural Changes

“…XeO 4 Isomers. According to our calculations (Table 1), the XeO 4 molecule optimized within T d symmetry is characterized by XeÀO = 1.75À1.81 Å, OÀO = 2.86À2.95 Å distances, the standard enthalpy of formation at 298 K varies in the range of 7.09À7.38 eV, fundamental frequencies are close to those reported from spectroscopy data, 2,3 and the calculated enthalpies of formation are compared with ΔH f θ 298 measured for gaseous XeO 4 in the reaction XeO 4 (g) f Xe(g) + 2O 2 (g) 21 (Table 1). As can be seen, the OPBE level of theory gives generally best predictions about geometry of the system, its fundamental frequencies, and enthalpy of formation.…”

Ultraviolet Photolysis Studies on XeO4 in Noble‐Gas and F2 Matrices and the Formation and Characterization of a New XeVIII Oxide, (η2‐O2)XeO3

“…All three oxides are thermodynamically unstable and shock‐sensitive. Xenon trioxide and XeO 4 decompose explosively to their elements with the release of 4021 and 642 kJ mol −1 ,2 respectively, whereas water‐insoluble XeO 2 decomposes at 0 °C over several minutes to Xe and O 2 3. Despite their hazardous natures, the molecular structures of XeO 3 and XeO 4 have been obtained from a single‐crystal X‐ray diffraction study on XeO 3 4 and an electron diffraction study on gaseous XeO 4 5.…”