We studied photodissociation dynamics of adenine dimer radical ions, A(2)(+), and hydrated adenine dimer ions, A(2)(+)(H2O)(n) (n = 1-6), at three wavelengths. The most abundant daughter ion is found to be protonated adenines, (AH)(+), which implies that proton transfer is followed by dissociation in A(2)(+) and A(2)(+)(H2O)(n). Theoretical calculations support that the most stable structures of A(2)(+) and A(2)(+)(H2O)(1) are formed by proton transfer. As cluster size of A(2)(+)(H2O)(n) becomes larger, the intensity of A(2)(+) as a daughter ion increases with the decrease in the intensity of (AH)(+). Upon photoexcitation of A(2)(+) by 266 nm, adenine monomer ion (A(+)) is also observed along with (AH)(+), which suggests that electronically excited states of (AH)(+) moiety in A(2)(+) promotes the hydrogen abstraction from (AH)(+). (C) 2007 Elsevier B.V. All rights reserved.