Thermochemistry of the higher chlorine oxides ClOx (x=3, 4) and Cl2Ox (x=3–7)†

Chlorates and perchlorates as potential high-energy materials: chlorate- and perchlorate-substituted methanes

The structures and properties of thirty-three of the thirty-four possible chlorato-Cl-, chlorato-O- and perchlorato-derivatives of methane have been computed using the range-separated hybrid generalized gradient approximation density functional method ωB97X-D with the 6-311+G(2d,p) basis set. These results indicate that the chlorato-O-substituent confers more stability to a molecule than does the chlorato-Cl-substituent; the perchlorato-substituent is approximately intermediate in this regard when decomposition energies are calculated. The C–Cl bond lengths in the chlorato-Cl-substituents generally elongate and the C–O distances in the chlorato-O- and perchlorato-substituents tend to shorten as the number of chlorate/perchlorate substituents increases. In addition, as the C–O bond shortens, the CO–Cl bond lengthens. The calculated Mulliken and Löwdin bond orders for these bonds exhibit the opposite of the trends exhibited by the bond lengths, as expected: As the bond lengthens, the bond order decreases, and vice versa. The single molecule that could not be optimized as a stable methane derivative, (chlorato-Cl-)tris(chlorato-O-)methane, rearranged during all optimization attempts to an isomer of the neutral Cl₂O₅ molecule and a hitherto unknown molecule, bis(chlorato-O-)carbonyl, (O₂ClO)₂C=O.

Thermochemistry and UV spectroscopy of alkyl peroxynitrates

High level ab initio calculations and multiconfigurational methods have been used to characterize the equilibrium structures, vibrational frequencies, enthalpies of formation, and UV-vis spectra of alkyl peroxynitrates R-OONO(2) (R = H, CH(3), C(2)H(5), C(3)H(7)). Excellent agreement with the experimental enthalpy of formation is obtained for HOONO(2) warranting similar accuracy for the rest of compounds for which values are inexistent or measured indirectly. The spectra obtained by MS-CASPT2/CASSCF calculations are very similar in all the species, showing a broad band below 200 nm with a shoulder due to pipi* transitions and a tail at approximately 250 nm due to weak npi* transitions on the NO(2) group.

Evidences for a new Ultraviolet Absorption Band of the FSO3 Radical

An unpublished absorption band of the fluorosulphate radical, FSO3, based on earlier experiments of Schumacher and co-workers (Z. Phys. Chem. NF 42 (1964) 174) and detailed calculations of the whole FSO3 spectra based on the time-dependent (TD) generalization of the density functional theory (DFT), TD-DFT, are reported. Part of this band, that increases in intensity at wavelengths below 275 nm, has been extracted from an absorption spectrum taken from equilibrated mixtures of FSO3 with the dimer FS(O2)OO(O2)SF at 403 K. A set of thirteen exchange-correlation hybrid functionals combined with the 6-311+G(3df) basis set predict an intense absorption band centred at 256 ± 10nm in very good agreement with the experimental observations. Another significant band peaked at 184 ± 10nm was also found. The calculations reproduce accurately the position of the maximum and the experimental oscillator strength of the well-known visible FSO3 band system.

Formation of Perfluorobutene-2 Epoxide in the Thermal Gas-Phase Reaction of Perfluorobutene-2 with Nitrogen Dioxide. An Experimental and DFT Study

The mechanism of the thermal reaction between perfluorobutene-2 and NO2 in the gas phase has been investigated in the temperature range 418.5–470.0K. At temperatures below 432K, equal amounts of perfluorobutene-2 epoxide (PFBE) and NO are formed. At higher temperatures, PFBE decomposes generating CF3C(O)F and CF3CF biradicals. The latter self-recombine reforming the parent perfluorobutene-2 molecule. The addition of O2 does not affect the reaction course. This reaction system provides a new and promising method for PFBE preparation. Based on the perfluorobutene-2 consumption, PFBE yields larger than 90% were obtained. The energetics of the relevant reaction pathways has been calculated using various density functional theory methods. These calculations confirm the reaction mechanism based on experimental results. The computed vibrational spectra predicted for the PFBE at the B3LYP/6-311+G(3df) and B98/6-311+G(3df) levels of theory are in very good agreement with that obtained experimentally.

Falloff Curves for the Recombination Reaction Cl + FC(O)O + M → FC(O)OCl + M

The pressure dependence of the recombination reaction Cl + FC(O)O + M --> FC(O)OCl + M has been investigated at 296 K. FC(O)O radicals and Cl atoms were generated by laser flash photodissociation of FC(O)OO(O)CF at 193 nm in mixtures with Cl2 and He or SF6 over the total pressure range 8-645 Torr. The measured FC(O)O radical and F atom yields in the photolysis are 0.33 +/- 0.06 and 0.67 +/- 0.06. The reaction lies in the falloff range approaching the high-pressure limit. The extrapolations toward the limiting low- and high-pressure ranges were carried out using a reduced falloff curves formalism, which includes a recent implementation for the strong-collision broadening factors. The resulting values for the low-pressure rate coefficients are (2.2 +/- 0.4) x 10(-28)[He], (4.9 +/- 0.9) x 10(-28)[SF6], (1.9 +/- 0.3) x 10(-28)[Cl2] and (5.9 +/- 1.1) x 10(-28)[FC(O)OO(O)CF] cm3 molecule(-1) s(-1). The derived high-pressure rate coefficient is (4.4 +/- 0.8) x 10(-11) cm3 molecule(-1) s(-1). For the reaction Cl + FC(O)OCl --> Cl2 + FC(O)O a rate coefficient of (1.6 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1) was determined. The high-pressure rate coefficient was theoretically interpreted using SACM/CT calculations on an ab initio electronic potential computed at the G3S level of theory. Standard heat of formation values of -99.9 and -102.5 kcal mol(-1) were computed at the G3//B3LYP/6-311++G(3df,3pd) level of theory for cis-FC(O)OCl and trans-FC(O)OCl, respectively. The computed electronic barrier for the conversion between the trans and cis conformers is 8.9 kcal mol(-1). On the basis of the present results, the above reactions are expected to have a negligible impact on stratospheric ozone levels.