Direct Observation of ClO from Chlorine Nitrate Photolysis

Abstract

Chlorine nitrate photolysis has been investigated with the use of a molecular beam technique. Excitation at both 248 and 193 nanometers led to photodissociation by two pathways, CIONO(2) --> CIO + NO()2 and CIONO(2) --> Cl + NO3, with comparable yields. This experiment provides a direct measurement of the CIO product channel and consequently raises the possibility of an analogous channel in CIO dimer photolysis. Photodissociation of the CIO dimer is a critical step in the catalytic cycle that is presumed to dominate polar stratospheric ozone destruction. A substantial yield of CIO would reduce the efficiency of this cycle.

Ultraviolet Photolysis of the ClO Dimer

“…Figure 2). Furthermore, for given O 3 and CH 4 concentrations, the ratio between Cl and ClO is determined by the ClO dimer photolysis, especially since the NO and O mixing ratios are low in the late winter lower stratosphere. In case a higher Cl mixing ratios are produced, which enhance the ozone destruction rate compared to case b.…”

“…Its atmospheric relevance was discussed by Eberstein and Minton et al 3,4 Several theoretical studies have been carried out to investigate the structure, stability, and photochemistry of the ClO dimer. [5][6][7][8][9][10] According to these works, Cl 2 O 2 occurs most likely in the stratosphere as dichlorine peroxide (ClOOCl), whereas other isomers, such as ClOClO or ClClO 2 , are believed to be less stable.…”

Photodissociation of bromobenzene at 266 nm

“…For example, nascent bromine atom will destroy ozone in the stratosphere via the BrO catalytic cycle 1 and it is mainly produced by solar ultraviolet ͑UV͒ photodissociation of natural, agricultural, and industrial bromocompounds. Photofragment translational spectroscopy ͑PTS͒ [2][3][4][5][6] has provided an ideal tool to investigate these photodissociation dynamics in a collision-free regime, in which any neutral photofragments ͑stable molecule or reactive radical͒ can be detected. In these experiments one can obtain product state, branching ratio, fragments translational energy distribution, and angular distribution of photofragments, thus one can get the energy distribution relationship between translational and internal energy.…”

Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation

“…Marinelli and Johnston detected NO 3 by absorption following ClONO 2 photolysis at 248 nm and reported a yield of 0.5 ± 0.3 for channel 1 [12]. More recently, Nelson et al investigated the photodissociation of ClONO 2 at 193 nm, 248 nm, and 308 nm using photofragment translational energy spectroscopy in a molecular beam [13][14][15]. The relative yields of channels 1 and 2 were calibrated using the photodissociation of Cl 2 O at 308 nm [16].…”