SearchPublisher and Institutes
You are here: Home :: Area NEM :: Chemistry :: Physical chemistry
Jürgen Troe
Are Primary Quantum Yields of NO2 Photolysis at λ ≤ 398 nm Smaller than Unity?
Primary quantum yields Φ of NO2 photolysis at wavelengths λ ≤ 398 nm and at bath gas pressures below 1 bar are analyzed. Stern-Volmer plots for collisional photolysis quenching, from experiments at pressures between 10 and 1000 bar, do not indicate a substantial reduction of the quantum yield below unity for pressures below 1 bar. The consequences of the recently discovered fluctuations of specific rate constants k(E) for NO2 dissociation on collisional photolysis quenching are analyzed. These effects can lead to a small reduction of Φ at pressures below 1 bar which, however, is also smaller than the reduction reported in some experiments. Reanalysis of these experiments shows instead that, apart from experimental artifacts, the influence of the secondary reactions O + NO2 (+ M) → NO3 (+ M), NO3 + NO → 2 NO2, and O + NO2 → O2 + NO was underestimated. As a consequence, all experimental evidence so far is in favour of a low pressure primary quantum yield which is unity over the complete wavelength range 300-398 nm. This leads to a revised recommendation of quantum yields Φ for the range 300-430 nm at 298 K and 248 K. A revision of the limiting low pressure rate constant at 298 K of the reaction O + NO2 + N2 → NO3 + N2 of (1.6&plusm;0.2)× 10-31 [N2] cm3 molecule-1 s-1 is also recommended (to be employed together with Fc = 0.6 and a limiting high pressure value of 2.2 × 10-11 cm3 molecule-1 s-1).
Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0942-9352
Volume: 214, 05/2000
Pages: 573