We study the gas-phase pyrolysis of benzyl azide (BA, C6H5CH2N3) using ultraviolet photoelectron spectroscopy (UVPES) and matrix-isolation infrared (IR) spectroscopy, together with electronic structure calculations and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. It is found that BA decomposes via N2 elimination at ca. 615 K, primarily yielding benzenemethaninime. Other end products include HCN and C6H6. N-Methyleneaniline is not detected, although its formation at higher temperature is foreseen by RRKM calculations.

The ozone-ethene reaction has been investigated at low pressure in a flow-tube interfaced to a u.v. photoelectron spectrometer. Photoelectron spectra recorded as a function of reaction time have been used to estimate partial pressures of the reagents and products, using photoionization cross-sections for selected photoelectron bands of the reagents and products, which have been measured separately. Product yields compare favourably with results of other studies, and the production of oxygen and acetaldehyde have been measured as a function of time for the first time. A reaction scheme developed for the ozone-ethene reaction has been used to simulate the reagents and products as a function of time. The results obtained are in good agreement with the experimental measurements. For each of the observed products, the simulations allow the main reaction (or reactions) for production of that product to be established. The product yields have been used in a global model to estimate their global annual emissions in the atmosphere. Of particular interest are the calculated global annual emissions of formaldehyde (0.96 ± 0.10 Tg) and formic acid, (0.05 ± 0.01 Tg) which are estimated as 0.04% and 0.7% of the total annual emission respectively.

The thermal decomposition of 2-H-heptafluoropropane, CF(3)CHFCF(3), at low pressure, heavily diluted in argon, has been studied over the temperature range 600-2000 degrees C using photoelectron spectroscopy. Comparison of the results obtained has been made with results of recent electronic structure calculations of possible decomposition pathways and results of a shock tube study. The most favored reaction thermodynamically, to produce CF(3)CF=CF(2) + HF, is found to be the main decomposition reaction at lower temperatures, 600-900 degrees C. At higher temperatures, 900-1200 degrees C, the decomposition reaction to give C(2)F(4) + CF(3)H was found to become important. No evidence for CF(3)CHFCF(3) --> CF(3)CHF + CF(3), a reaction expected to be important from a shock tube study, performed at much higher pressures, or for CF(3)CHFCF(3) --> CF(3)CF + CF(3)H was obtained, although for the latter reaction it is likely that CF(3)CF converts into C(2)F(4) under the conditions used before photoionization, in the ionization region of the photoelectron spectrometer. At higher temperatures C(3)F(6) decomposes to C(2)F(4) + CF(2), and C(2)F(4) decomposes to CF(2). Ab initio calculations have been performed of the adiabatic and vertical ionization energies of possible primary pyrolysis products to assist assignment of the photoelectron spectra recorded for heated flowing gas samples. A comparison is made between the threshold photoelectron spectrum and the photoelectron spectrum of CF(3)CF=CF(2).

The UV photoelectron spectrum of CF(3)CHF(2) has been recorded and assigned using EOM-CCSD calculations. For the first band, the adiabatic ionization energy (AIE) and vertical ionization energy (VIE) have been measured as (12.71 +/- 0.05) and (13.76 +/- 0.02) eV, respectively. The measured AIE is higher than the recommended value from state-of-the-art ab initio calculations of (12.26 +/- 0.02) eV because of a large geometry change on ionization, mainly arising from a significant increase in the C-C bond length, which results in poor Franck-Condon factors in the adiabatic region. The experimental VIE also shows poor agreement with the computed value of 14.05 +/- 0.06 eV because, in the higher energy region of the first photoelectron band, dissociation of CF(3)CHF(2)(+) to CHF(2)(+) + CF(3) occurs. This has a calculated thermodynamic onset of (12.89 +/- 0.20) eV. Recommendations are made for the heats of formation, DeltaH(f,298)(slashed circle), of CF(3)CHF(2) and CF(3)CHF(2)(+), based on the results of the ab initio calculations. Pyrolysis of flowing CF(3)CHF(2) diluted in argon shows evidence of production of C(2)F(4) and HF at lower temperatures and CF(2) and CF(3)H at higher temperatures. The relative temperature dependence of the observed photoelectron bands associated with these molecules is interpreted in terms of two decomposition reactions of CF(3)CHF(2) as well as the reaction C(2)F(4) --> 2CF(2).