GVVPT2 multireference perturbation theory study of selenium oxides

Abstract

The electronic structures of oxides of selenium, SeO, SeO₂, and SeO₃, and their dimers, Se₂O₃ and Se₂O₅, were studied using the second-order Generalised van Vleck variant of multireference perturbation theory (GVVPT2), with comparison to the linked completely renormalised coupled cluster through perturbative triple excitations, i.e., CR-CC(2,3), theory. Geometry optimisations of SeO, SeO₂, and SeO₃ using GVVPT2 and the cc-pVTZ basis set show close agreement with CR-CC(2,3) results and, for SeO and SeO₂, close agreement with experiment. In contrast, both GVVPT2 and CR-CC(2,3) predict that the r _e bond length of SeO₃ is significantly shorter (ca. 0.1 Å) than the r ₀ experimental value. Calculations of energies of oxidation reactions predict the formation of SeO₂ and SeO₃ from SeO to be exothermic. The geometries and energetics of four isomers of both Se₂O₃ and Se₂O₅ have been characterised using a composite methodology; key transition states between the isomers were similarly calculated. Because of comparable energies, and relatively low transition barrier heights, several isomers of the dimeric species are predicted to be chemically relevant. Harmonic vibrational frequencies of monomeric and dimeric selenium oxides were obtained at the B3LYP/6-311G^* level of theory and corroborate geometrical data that many of the characteristics of the monomeric selenium oxides are preserved in the dimeric species.

Keywords:

• multireference perturbation theory
• electronic structure theory
• metalloid oxides

Acknowledgements

The authors gratefully acknowledge the DOE Office of Science under Award Number DE-FG02-06ER46292 for partial financial support of the research presented herein. W.J. and Z.C. acknowledge NSF Grant Number EPS-0814442 for a Doctoral Dissertation Assistantship and Postdoctoral Research Assistantship, respectively. D.K. thanks the NSF REU programme (Grant Number CHE-0850644).

Notes

^aRef. [58]; ^bRef. [59].

^aRef. [59]; ^bRef. [62]; ^c r₀ (Se–O) from Ref. [17].

^aExperimental enthalpies of the reactions Se + O₂ → SeO + O (18.2 kcal/mol) and SeO + O₂ → SeO₂ + O (18.85 kcal/mol) from [13] were recalculated using the enthalpy of formation of atomic oxygen (59.55 kcal/mol) from JANAF Tables (Ref. [60]).

^aRef. [61]; ^bRef. [63].