Structural and Mechanistic Analysis through Electronic Spectra: Aqueous Hyponitrite Radical (N2O2-) and Nitrosyl Hyponitrite Anion (N3O3-)

Journal Article · Thu Nov 03 00:00:00 EDT 2011 · Journal of Physical Chemistry A

DOI:https://doi.org/10.1021/jp204967h· OSTI ID:1030472

Valiev, Marat; Lymar, Sergei V

Aqueous hyponitrite radical (N{sub 2}O{sub 2}{sup -}) and nitrosyl hyponitrite anion (N{sub 3}O{sub 3}{sup -}) species 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=NO{sub 2}{sup -}), the trans configuration of the resulting ON=NO{sup -} radical is preserved; (2) although cis- and trans-ON=NO{sup -} are energetically nearly equivalent, the barrier for the trans-cis isomerization is prohibitively high due to the partial double character of the NN bond; (3) the UV spectrum of ON=NO{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 is the dominant observable species, and the asymmetric isomer contributes little to the experimental spectrum. Coherent analysis of the calculated and experimental data suggests a re-interpretation 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 Khom = 2.2 - 10{sup -7} M. Collectively, these results demonstrate that advanced theoretical modeling can be of significant benefit in structural and mechanistic analysis of UV spectra.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1030472
• Report Number(s): PNNL-SA-80255; 34900; KC0301020; TRN: US201124%%233
• Journal Information: Journal of Physical Chemistry A, Vol. 115, Issue 43
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTRA
ANIONS
CHEMISTRY
CONFIGURATION
ISOMERIZATION
ISOMERS
OXIDATION
RADICALS
RADIOLYSIS
REACTION KINETICS
SIMULATION
SPECTRA
aqueous hyponitrite radical
nitrosyl hyponitrite anion
spectra
isomers
quantum mechanical calculations
cis-sodium hyponitrite
nitric-oxide
molecular-dynamics
density
nitroxyl
energy
reduction
Environmental Molecular Sciences Laboratory