Transient raman spectra, structure and thermochemistry of the selenocyanate dimer radical anion in water

Janik, Ireneusz

Permalink

https://hdl.handle.net/2142/100496 Copy

Description

Title

Transient raman spectra, structure and thermochemistry of the selenocyanate dimer radical anion in water

Author(s)

Janik, Ireneusz

Contributor(s)

Tripathi, G. N. R.

Issue Date

2018-06-22

Keyword(s)

Vibrational structure/frequencies

Abstract

Time-resolved resonance-enhanced Raman spectra of the selenocyanate dimer radical anion, (SeCN)2 .−, prepared by pulse radiolysis in water, have been obtained and interpreted in conjunction with theoretical calculations to provide detailed information on the molecular geometry and bond properties of the species. The structural properties of the radical are used to develop a molecular perspective on its thermochemistry in aqueous solution. Twelve Stokes Raman bands of the radical observed in the 100-3000cm−1 region are assigned in terms of the strongly 140.5cm−1 , weakly 550cm−1 , and moderately 2095cm−1 , enhanced fundamentals, their overtones and combinations. Calculations by range-separated hybrid density functionals (ωB97x and LC-ωPBE) support the spectroscopic assignments of the 140.5cm−1vibration to a predominantly SeSe stretching mode and the features at 550cm−1 and 2095cm−1 to SeC and CN symmetric stretching modes, respectively. The corresponding bond lengths are 2.957A, 1.823 ˚ Aand 1.157 ˚ A. A first order anharmonicity of ˚ 0.44cm−1determined for the SeSe stretching mode suggests a convergence of vibrational states at an energy 1.4eV, using the Birge–Sponer extrapolation. This value, estimated for the radical confined in solvent cage, compares well with the calculated gas-phase energy, 1.32eV, required for the radical to dissociate into SeCN. and SeCN− fragments. The enthalpy of dissociation drops to 0.70eV in water when solvent dielectric effects on the radical and its dissociation products upon SeSe bond scission are incorporated in the calculations. Our findings are compared to analogous symmetric and asymmetric hemibonded radical anions i.e. (SCN)2 .− and NCSOH.− to provide insights into relationship between their structure and properties.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100496

DOI

10.15278/isms.2018.FA05

Copyright and License Information

Copyright 2018 Ireneusz Janik

Owning Collections