Near ultraviolet photodissociation spectroscopy of Mn(+)(H2O) and Mn(+)(D2O).

Abstract

The electronic spectra of Mn(+)(H2O) and Mn(+)(D2O) have been measured from 30,000 to 35,000 cm(-1) using photodissociation spectroscopy. Transitions are observed from the (7)A1 ground state in which the Mn(+) is in a 3d(5)4s(1) electronic configuration, to the (7)B2 (3d(5)4py) and (7)B1 (3d(5)4px) excited states with T0 = 30,210 and 32,274 cm(-1), respectively. Each electronic transition has partially resolved rotational and extensive vibrational structure with an extended progression in the metal-ligand stretch at a frequency of ∼450 cm(-1). There are also progressions in the in-plane bend in the (7)B2 state, due to vibronic coupling, and the out-of-plane bend in the (7)B1 state, where the calculation illustrates that this state is slightly non-planar. Electronic structure computations at the CCSD(T)/aug-cc-pVTZ and TD-DFT B3LYP/6-311++G(3df,3pd) level are also used to characterize the ground and excited states, respectively. These calculations predict a ground state Mn-O bond length of 2.18 Å. Analysis of the experimentally observed vibrational intensities reveals that this bond length decreases by 0.15 ± 0.015 Å and 0.14 ± 0.01 Å in the excited states. The behavior is accounted for by the less repulsive px and py orbitals causing the Mn(+) to interact more strongly with water in the excited states than the ground state. The result is a decrease in the Mn-O bond length, along with an increase in the H-O-H angle. The spectra have well resolved K rotational structure. Fitting this structure gives spin-rotation constants ɛaa″ = -3 ± 1 cm(-1) for the ground state and ɛaa' = 0.5 ± 0.5 cm(-1) and εaa' = -4.2 ± 0.7 cm(-1) for the first and second excited states, respectively, and A' = 12.8 ± 0.7 cm(-1) for the first excited state. Vibrationally mediated photodissociation studies determine the O-H antisymmetric stretching frequency in the ground electronic state to be 3658 cm(-1).