Dynamics of electron attachment and photodissociation in iodide-uracil-water clusters via time-resolved photoelectron imaging.

The dynamics of low energy electron attachment to monohydrated uracil are investigated using time-resolved photoelectron imaging to excite and probe iodide-uracil-water (I−·U·H2O) clusters. Upon photoexcitation of I−·U·H2O at 4.38 eV, near the measured cluster vertical detachment energy of 4.40 eV ± 0.05 eV, formation of both the dipole bound (DB) anion and valence bound (VB) anion of I−·U·H2O is observed and characterized using a probe photon energy of 1.58 eV. The measured binding energies for both anions are larger than those of the non-hydrated iodide-uracil (I−·U) counterparts, indicating that the presence of water stabilizes the transient negative ions. The VB anion exhibits a somewhat delayed 400 fs rise when compared to I−·U, suggesting that partial conversion of the DB anion to form the VB anion at early times is promoted by the water molecule. At a higher probe photon energy, 3.14 eV, I− re-formation is measured to be the major photodissociation channel. This product exhibits a bi-exponential rise; it is likely that the fast component arises from DB anion decay by internal conversion to the anion ground state followed by dissociation to I−, and the slow component arises from internal conversion of the VB anion. [ABSTRACT FROM AUTHOR]