Reactions of H⁺(pyridine)_<i>m</i>(H₂O)_<i>n</i> and H⁺(NH₃)₁(pyridine)₁(H₂O)_<i>n</i> with NH₃: experiments and kinetic modelling under tropospheric conditions

Abstract

Abstract. Reactions between pyridine containing water cluster ions, H+(pyridine)1(H2O)n, H+(pyridine)2(H2O)n and H+(NH3)1(pyridine)1(H2O)n (n up to 15) with NH3 have been studied experimentally using a quadrupole time-of-flight mass spectrometer. The product ions in the reaction between H+(pyridine)m(H2O)n and NH3 have been determined for the first time. It is found that the reaction mainly leads to cluster ions of the form HH+(NH3)1(pyridine)1(H2O)n−x, with x = 1 or 2 depending on the initial size of the reacting cluster ion. For a given number of water molecules (from 5 to 15) in the cluster ion, rate coefficients are found to be slightly lower than those for protonated pure water clusters reacting with ammonia. The rate coefficients obtained from this study are used in a kinetic cluster ion model under tropospheric conditions. The results from the model suggest that cluster ions containing ammonia and more than one pyridine, picoline or lutidine molecule should dominate at ground level under typical conditions.