PHOTODISSOCIATION OF (A)OVER-TILDE ((2)A(2))-EXCITED OCLO AND ITS AGGREGATES

Photofragmentation of chlorine dioxide (OClO) and its aggregates is in vestigated in the UV regime [349-373 nm, (A) over tilde((2)A(2)) <-- ( X) over tilde(B-2(1)) transition]. The products of UV photolysis are s ubsequently ionized with vacuum UV laser radiation followed by time-of -flight mass analysis. The isolated molecule decays predominantly by f ormation of vibrationally excited ClO (X((II)-I-2)) as a result of pre dissociation. Highly vibrationally excited ClO is formed if even quant a of the asymmetric stretching vibration are excited. The results are discussed in relation to the UV absorption cross section and competiti ve fragmentation routes, such as formation of molecular oxygen. The UV photolysis of homogeneous chlorine dioxide aggregates [(OClO)(n)] yie lds fragments such as excited molecular oxygen, Cl2O3, and Cl3O5. Evid ence for evaporation of neutral molecules from excited aggregates is f ound as well. The results on aggregate photolysis are discussed in rel ation to experiments on chlorine dioxide in the gas and condensed phas e. Ab initio calculations are performed in order to rationalize the ex perimental results. Properties, such as structures, stabilities, and v ibrational frequencies, of different isomers of the OClO dimer and the photolysis product Cl2O3 are derived. Possible implications to strato spheric photochemistry are briefly discussed.