NO3 Photolysis Product Channels: Quantum Yields from Observed Energy Thresholds
Abstract
The absorption of visible light by NO 3 leads to three products: NO + O 2, NO 2 + O, and fluorescence. We report a new method for obtaining quantum yields for the NO 3 molecule, using measured energy thresholds separating NO 3 and its product channels. The assumptions of this model are the following: (i) NO 3 internal energy (photon plus vibrations plus rotations) gives the necessary and sufficient condition to select each of the three product channels, as justified by the observed large differences in reaction times for the three products. (ii) The unresolved complexities of ground-state NO 3 spectra and quantum states are approximated by standard separable ro-vibrational expressions for statistical mechanical probability functions. These results may be of interest to both physical chemists and atmospheric chemists. The NO 3 * vibronic precursors of the three product channels are identified. We evaluate and plot vibrational state-specific absolute quantum yields as a function of wavelength Φ vib (λ) for each product channel. We sum over vibrational states to give the macroscopic quantum yield as a function of wavelength Φ(λ), obtained here from 401 to 690 nm and at 190, 230, and 298 K. By adding considerations of light absorption cross sections σ(λ) at 230 and 298 K and a stratospheric radiation distribution I (λ) from 401 to 690 nm, we evaluate the wavelength dependent photochemical rate coefficients j (λ) for each of the three product channels, and we find the integrated…
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