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Title: The selenocyanate dimer radical anion in water: Transient Raman spectra, structure, and reaction dynamics

Journal Article · · Journal of Chemical Physics
DOI:https://doi.org/10.1063/1.5086400· OSTI ID:1609174
ORCiD logo [1];  [1]
  1. Univ. of Notre Dame, IN (United States)
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The selenocyanate dimer radical anion (SeCN)2•-, prepared by electron pulse irradiation of selenocyanate anion (SeCN)⁻ in water, has been examined by transient absorption, time-resolved Raman spectra, and range-separated hybrid density functional (ωB97x and LC-ωPBE) theory. The Raman spectrum, excited in resonance with the 450 nm (λmax) absorption of the radical, is dominated by a very strong band at 140.5 cm⁻¹, associated with the Se–Se stretching vibration, its overtones and combinations. A striking feature of the (SeCN)2•- Raman spectrum is the relative sharpness of the 140.5 cm⁻¹ band compared to the S–S band at 220 cm⁻¹ in thiocyanate radical anion (SCN)2•-, the difference of which is explained in terms of a time-averaged site effect. Calculations, which reproduce experimental frequencies fairly well, predict a molecular geometry with the SeSe bond length of 2.917 (±0.04) Å, the SeC bond length of 1.819 (±0.004) Å, and the CN bond length of 1.155 (±0.002) Å. An anharmonicity of 0.44 cm⁻¹ has been determined for the 140.5 cm⁻¹ Se–Se vibration which led to a dissociation energy of -1.4 eV for the SeSe bond, using the Morse potential in a diatomic approximation. This value, estimated for the radical confined in a solvent cage, compares well with the calculated gas-phase energy, 1.32 ± 0.04 eV, required for the radical to dissociate into (SeCN)• and (SeCN)⁻ fragments. Here, the enthalpy of dissociation in water has been measured (0.36 eV) and compared with the value estimated by accounting for the solvent dielectric effects in structural calculations.

Research Organization:
University of Notre Dame, IN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
Grant/Contract Number:
FC02-04ER15533
OSTI ID:
1609174
Journal Information:
Journal of Chemical Physics, Vol. 150, Issue 9; ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 4 works
Citation information provided by
Web of Science

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