A new model of N_2O quantum yield in the UV photolysis of O_3/O_2/N_2 mixtures: Contributions of electronically excited O3 and O_3(centre dot)N_2

摘要

Electronically excited O_3 and O_3(centre dot)N_2 dimer are proposed as contributors to the N_2O quantum yield, #phi#_(N2O), following UV photlysis of O_3 in O_3/O_2/N_2 mixture. At 100 to 900 torr N_2 pressures, #phi#_(N2O) is dominated by the electronically excited O_3. In this pressure regime #phi#_(N2O) in the 310<=#lambda#<=340 nm region could, potentially, exceed #phi#_(N2O) in the #lambda#<310 nm region. The "classical" O(~1D), N_2 association predominates above 10 atm. The O+2(centre dot)N_2+hv may dominate at high pressures (>=500 atm) if the temperature is very low (<=50 K). The atmospheric importance of N_2O production via the classical mechanism is well known to be insignificant. In contrast, the production from excited O_3 appears to have the potential to significantly affect or current understandings of stratospheric coupled NO_x-O_3 chemistry and the climatologically important N_2O source-sink budget. It is therefore critical to determine the wavelength variation of #phi#_(N2O) in the 310<=#lambda#<=340 nm region by gas phase experiments. Theoretical studies are needed to understand, a the quantum chemistry level, the mechanism of the suggested N_2O formation from ultra-short-lived electronically excited O_3.