Photodissociation of ICN at the liquid/vapor interface of water

Abstract

The photodissociation of ICN adsorbed at the liquid/vapor interface of water is studied using classical molecular dynamics with nonadiabatic surface hopping. The cage escape, geminate recombination to form ICN and INC and the subsequent vibrational relaxation of these two molecules (on their ground electronic states) is compared with the same process in bulk water and with previous photodissociation studies at liquid interfaces. We find that the reduced surface density and weaker solvent-solute interactions give rise to reduced rate of nonadiabatic transitions and that the probability for cage escape at the interface is significantly enhanced due to the possibility that one or both of the photodissociation fragments desorb into the gas phase. The overall desorption probability varies from 75% to 92% for ICN initially located just below the Gibbs surface (50% bulk density) to ICN located just above the Gibbs surface, respectively. The corresponding geminate recombination probabilities are 18% and 9%, respectively. The vibrational relaxation rate of the recombined ICN is slower than in the bulk by a factor of 2.3.

Enhanced surface photochemistry in chloride–nitrate ion mixtures

“…16 One potential explanation for this surprising result is that when chloride is present, nitrate ions are closer to the interface where a reduced solvent cage can lead to enhanced escape of nitrate ion photofragments such as NO 2 into the gas phase. For example, theoretical calculations by Benjamin and coworkers 48,50 suggest that photolysis of ICN at the interface leads to enhanced desorption of the photoproducts into the gas phase relative to photolysis of bulk ICN solutions due to reduced trapping by an incomplete solvent cage at the surface, and there is experimental evidence for surface-enhanced photolysis as well. 46,47,51 …”

“…45 Such reduced solvent cages may result in enhanced quantum yields at the interface. [46][47][48][49][50] For example, the photolysis of Mo(CO) 6 was observed to be at least three orders of magnitude faster when dispersed in droplets compared to that for the bulk solution. 51 In the case of nitrate-chloride ion mixtures, the OH radical generated in reaction (1a) can potentially oxidize chloride ions to Cl 2 .…”

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

“…10 There is increasing evidence, both theoretical and experimental, that the quantum yields for photolysis at interfaces are indeed significantly greater than in the bulk. [159][160][161][162][163][164][165][166][167][168] …”

The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

“…15,16 There is also evidence that the photolysis of species at the interface has higher quantum yields than those in the bulk. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] In short, interfacial kinetics and mechanisms may be significantly different compared to those in the bulk phase.…”