Ab Initio Study of Pernitric Acid: Comparison with Experimental Spectra

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.

Thermal Decomposition of HO2NO2 (Peroxynitric Acid, PNA): Rate Coefficient and Determination of the Enthalpy of Formation

Rate coefficients for the gas-phase thermal decomposition of HO(2)NO(2) (peroxynitric acid, PNA) are reported at temperatures between 331 and 350 K at total pressures of 25 and 50 Torr of N(2). Rate coefficients were determined by measuring the steady-state OH concentration in a mixture of known concentrations of HO(2)NO(2) and NO. The measured thermal decomposition rate coefficients k(-)(1)(T,P) are used in combination with previously published rate coefficient data for the HO(2)NO(2) formation reaction to yield a standard enthalpy for reaction 1 of Delta(r)H degrees (298K) = -24.0 +/- 0.5 kcal mol(-1) (uncertainties are 2sigma values and include estimated systematic errors). A HO(2)NO(2) standard heat of formation, Delta(f)H degrees (298K)(HO(2)NO(2)), of -12.6 +/- 1.0 kcal mol(-1) was calculated from this value. Some of the previously reported data on the thermal decomposition of HO(2)NO(2) have been reanalyzed and shown to be in good agreement with our reported value.

High level ab initio study of the structure and vibrational spectra of HO2NO2

A high-level ab initio study has been performed on the conformational structure and vibrational spectra of HO(2)NO(2). Calculations carried out with coupled-cluster methods using a series of Pople and Dunning basis sets reveal that there is a significant basis set dependence on the predicted ab initio structure. Higher angular momentum basis sets are shown to be necessary in order to bring the calculated structure into agreement with experimental rotational constants. Harmonic vibrational frequencies of HO(2)NO(2) are computed at the CCSD(T)/aug-cc-pVTZ level of theory while the corresponding vibrational anharmonicities are calculated at the MP2/cc-pVTZ level. In addition, the absorption cross sections of OH stretching overtones in HO(2)NO(2) are calculated using a dipole function computed at the QCISD level of theory and found to be in good agreement with the available experimental data.