Abstract. The heterogeneous interaction of the stratospheric reservoir species HC1, C1ONO2, and N20 s with water-rich polar stratospheric particle mimics is characterized by the formation of solvated ionic products. Simple semiempirical calculations have been used to explain the nature of the species observed in infrared spectroscopic measurements and to elucidate the mechanism by which they are formed. The initial stages of the interaction appear to involve an SN2-type nucleophilic attack by the oxygen atom of the surface water molecule upon the most accessible electrophilic site of the adsorbing reactant. Mechanistic schemes involving protonated acid intermediates and their subsequent decomposition or hydrolysis can be used to accurately predict and explain the stable reaction products observed spectroscopically under stratospheric conditions.

The adsorption of DCI, CCI,, CFCI,, CF2C12 and CF,CI on thin D20 ice films at 110 K has been studied using reflection-absorption infrared spectroscopy (RAJRS). These compounds interact to varying degrees with the ice surface via the OD bonds dangling into the vacuum. DCI was found to dissociate ionically, evidenced by a strong band attributable to D30+ and the absence of any absorption band for molecular DCI.

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In this article, we describe a series of experiments investigating the interaction of the important stratospheric reservoir species HCl with the surface of a thin ice film. Reflection absorption infrared spectroscopy and thermal desorption spectroscopy have been used to identify the nature of the ionic hydrates formed under a variety of pressure, temperature, and exposure regimes.