Clusters of atmospheric relevance: H(2)O/HCl/HNO(3). Prediction of IR & MW spectra.

Theoretical calculations at the B3LYP/aug-cc-pVQZ level are performed on ternary clusters of water, hydrogen chloride and nitric acid to predict their IR and MW spectra. The main IR spectral features and their changes in a set of 15 selected clusters are analyzed in terms of the different hydrogen bonding characteristics of the aggregates. The formation of these clusters in laboratory experiments and their possible identification based on their infrared and microwave spectral properties are discussed. Based on a calculation of the Gibbs free-energy of formation of the clusters from their monomers, the population distribution of the molecules at atmospherically relevant temperatures is evaluated, and the IR spectra of the composed mixture are predicted. The variations of specific spectral features with temperature are assessed, and the possible observation of these features is proposed as a means to detect the existence of these clusters, as well as an indication of the temperature of the corresponding atmospheric sample.