The mechanism for ultraviolet photolysis of gaseous chlorine nitrate at 302.5 nm

Abstract

The laboratory photolysis of chlorine nitrate (ClONO 2 ) with 302.5 nm ultraviolet light leads to the destruction per quantum of 4 molecules of ClONO 2 and the formation of 1 molecule of O 2 , 2 of Cl 2 and 2 of N 2 O 5 . These quantum yields are not consistent with the current assumption that the primary photolysis step for ClONO 2 in the stratosphere leads to the formation of ClO plus NO 2 . A consistent mechanism exists in which the photolytic step involves the decomposition of ClONO 2 to ClONO + O(³P). The onset of observed absorption of radiation by ClONO 2 corresponds approximately to the thermodynamic accessibility of this simple splitting away of an O atom. The photolysis of ClONO occurs very rapidly in the stratosphere, either to Cl + NO 2 or ClO + NO. The substitution of either Cl + NO 2 + O or ClO + NO + O for ClO + NO 2 as the eventual photolysis products from ClONO 2 is not expected to cause appreciable alteration in predictions from stratospheric modeling.