Structural and Mechanistic Analysis through Electronic Spectra: Aqueous Hyponitrite Radical (N(2)O(2)(-)) and Nitrosyl Hyponitrite Anion (N(3)O(3)(-))
Aqueous hyponitrite radical (N{sub 2}O{sub 2}{sup -}) and nitrosyl hyponitrite anion (N{sub 3}O{sub 3}{sup -}) are important intermediates in the reductive chemistry of NO. The structures and absorption spectra of various hydrated isomers of these compounds were investigated in this work using high-level quantum mechanical calculations combined with the explicit classical description of the aqueous environment. For N{sub 2}O{sub 2}{sup -}, comparison of the calculated spectra and energetics with the experimental data reveals that (1) upon the one-electron oxidation of trans-hyponitrite (ON{double_bond}NO{sup 2-}), the trans configuration of the resulting ON{double_bond}NO{sup -} radical is preserved; (2) although cis- and trans-ON{double_bond}NO{sup -} are energetically nearly equivalent, the barrier for the trans-cis isomerization is prohibitively high because of the partial double character of the NN bond; (3) the calculations confirm that the UV spectrum of ONNO{sup -} was misinterpreted in the earlier pulse radiolysis work, and its more recent revision has been justified. For the N{sub 3}O{sub 3}{sup -} ion, the symmetric isomer the dominant observable species, and the asymmetric isomer contributes insignificantly to the experimental spectrum. Coherent analysis of the calculated and experimental data suggests a reinterpretation of the N{sub 2}O{sub 2}{sup -} + NO reaction mechanism according to which the reaction evenly bifurcates to yield both the symmetric and asymmetric isomers of N{sub 3}O{sub 3}{sup -}. While the latter isomer rapidly decomposes to the final NO{sub 2}{sup -} + N{sub 2}O products, the former isomer is stable toward this decomposition, but its formation is reversible with the homolysis equilibrium constant K{sub hom} = 2.2 x 10{sup -7} M. Collectively, these results demonstrate that advanced theoretical modeling can be of significant benefit in structural and mechanistic analysis on the basis of the electronic spectra of aqueous transients.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE SC OFFICE OF SCIENCE (SC)
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1041603
- Report Number(s):
- BNL-95268-2012-JA; R&D Project: CO-004; KC0301010; TRN: US201212%%21
- Journal Information:
- The Journal of Physical Chemistry A, Vol. 115, Issue 43
- Country of Publication:
- United States
- Language:
- English
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