EXPERIMENTAL AND THEORETICAL-STUDY OF THE REACTION OF HO- WITH NO

Hydroxide ion (HO-) reacts with nitric oxide by slow reactive electron detachment wit a rate coefficient approximately 4 X 10(-12) cm3 s-1 a t 298 K. The detachment process is presumably associative detachment f orming nitrous acid and an electron. Observations, data analysis, and alternative explanations for these observations are discussed. The ass ociative detachment reaction was also investigated theoretically throu gh calculations of the geometries, relative energies, and normal-mode vibrational frequencies of the relevant species HO-, HO, NO, cis- and trans-HONO, and cis- and trans-HONO-. These calculations indicate that in the ion HONO-, the cis conformer is more stable, while in the neut ral HONO, the trans conformer is more stable. The HO-NO bond in HONO, which is formed in this reaction, is much stronger than the HO--NO bon d in HONO- with an energy of 198.7 +/- 1.8 kJ mol-1 for cis-HONO [J. P hys. Chem. Ref. Data 14, 1 (1985)] and 52.2 +/- 5 kJ mol-1 for cis-HON O-at 0 K. HONO- is bound with respect to HONO. The adiabatic electron detachment energy resulting from detachment from cis-HONO- forming the same conformer of the neutral molecule cis-HONO is 0.29+/-0.05 eV. Th e HO-NO equilibrium bond distance in HONO- is considerably longer than that in HONO, with values of 1.750 and 1.640 angstrom for trans- and cis-HONO-, respectively, and 1.429 and 1.392 angstrom for trans- and c is-HONO, respectively. These geometric and energetic characteristics o f HONO- and HONO are combined with calculations of relative energies o f these species at nonequilibrium/distorted HO-NO bond lengths to give a qualitative picture of the potential energy curves for these specie s along the reaction coordinate. While no significant energy barrier t o autodetachment of HONO- is present, the Franck-Condon wave function overlap for autodetachment is small and is likely the reason for the o bserved inefficiency. The maximum calculated rate constant for associa tive detachment is 4 X 10(-12) CM3 S-1, in good agreement with the obs erved value.