title: Photoinduced oxidation of water in the pyridine-water complex: comparison of the singlet and triplet photochemistries.
abstract: It has recently been shown that low-lying dark charge-separated singlet excited states of nπ* and ππ* character exist in the hydrogen-bonded pyridine-water complex in addition to the familiar nπ* and ππ* excited states of the pyridine chromophore. The former have been shown to promote the transfer of a proton from water to pyridine, resulting in the pyridinyl-hydroxyl radical pair. In the present work, the potential-energy surfaces of the triplet excited states of the pyridine-water complex have been explored with the same ab initio electronic-structure methods (ADC(2), CASPT2). Minimum-energy reaction paths for excited-state H atom transfer, energy surfaces in the vicinity of the barrier for H atom transfer, as well as multistate surface crossings have been characterized. The photochemical reaction mechanisms on the singlet and triplet potential-energy surfaces are compared, and their relevance for photoinduced water oxidation with the pyridine chromophore are discussed.
authors.affiliation: Department of Chemistry, Technische Universität München , D-85747 Garching, Germany.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Liu
authors.forename: Andrzej L
authors.initials: AL
authors.lastname: Sobolewski
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Domcke