Effect of dissociation on the reactivity and inhibition capacity of p-nitro-phenol towards ortho-positronium in methanol solutions

The effect of dissociation on the reactivity and inhibition capacity of p-nitro-phenol /p-NPH/ towards orthopositronium atom has been investigated by performing positron lifetime measurements in methanol and methanol containing 0.5M NaOH solutions, respectively. In the latter case the solute exists in anionic form /p-NP^–/. It has been found that as a result of dissociation, both the rate constant /k/ and the inhibition coefficient // decrease significantly. Their values are k=/7.5±0.4/×10⁸ s^–1 M^–1 and =6.8±0.2 M^–1 for p-NPH and k_d=/0.6±0.2/×10⁸ s^–1 M^–1 and _d=4.0±0.2 M^–1 for p-NP^–. The possible reasons for these effects are discussed.