Femtosecond spectroscopy of the dissociation and geminate recombination of aqueous carbon disulfide

Summary form only given. Ultrafast spectroscopy on small molecules in solution offers a unique possibility for studying solvent-solute interaction, since the spectroscopic properties of the species involved often are well determined. In this context, photodissociation of tri-atomic molecules stands out as being particularly interesting, since the dissociation of these species may follow several different solvent dependent reaction paths, while still being simple enough to allow for high level calculations of the reaction dynamics. A potentially very interesting triatomic molecule is CS/sub 2/. When gas-phase CS/sub 2/ is photolyzed at 193 nm (6.4 eV), it dissociates into CS and S. Approximately 50% of the available energy goes to CS rotation and vibration, while the remaining 0.4 eV or 1.0 eV (depending on the electronic state of the S atom) is transferred to the fragments as kinetic energy. In the work we photo-dissociate CS/sub 2/ in aqueous solution at 200 nm and measure the presence of the products with 0.5 ps time resolution in the spectral range from 200 nm to 400 nm. The measurements show a close to 100% geminate recombination of the CS and S fragments caused by caging by the surrounding water molecules. Following geminate recombination, CS/sub 2/ is formed vibrationally hot and the molecule relaxes to the vibrational groundstate within 200 ps.