Abstract
Abstract. The optimized structures and proton affinities of a total of 81 nitrogen-containing bases, chosen based on field measurements of ambient positive ions, were studied using the CBS-QB3 quantum chemical method. The results were compared to values given in the National Institute of Standards and Technology (NIST) Chemistry WebBook in cases where a value was listed. The computed values show good agreement with the values listed in NIST. Grouping the molecules based on their molecular formula, the largest calculated proton affinities for each group were also compared with experimentally observed ambient cation concentrations in a boreal forest. This comparison allows us to draw qualitative conclusions about the relative ambient concentrations of different nitrogen-containing organic base molecules.
Highlights
Electric charge plays a central role in atmospheric sciences
Grouping the molecules based on their molecular formula, the largest calculated proton affinities for each group were compared with experimentally observed ambient cation concentrations in a boreal forest
In the case of pyridine, all results were compared to the proton affinity (PA) value listed in National Institute of Standards and Technology (NIST)
Summary
Sample ionization is employed in many measurement devices such as the chemical ionization mass spectrometer (CIMS) (Eisele and Tanner, 1991). This is because ionizing the sample makes it possible to detect particles of smaller sizes than what could have been measured had the sample remained neutral. In order to relate such measurement results to actual atmospheric conditions, we need to understand the possible effects of the ionization process on the molecules or clusters being charged as well as on the chemistry of the ionized sample. An easy way of assessing this question is to examine the proton affinities of molecules
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