Absorption of infra-red radiation by atmospheric molecular cluster- ions

Results from previous laboratory experiments indicate that both the protonated water dimer H3O(H2O), and molecular cluster-ions, X(H2O)n absorb infra-red (IR) radiation in the water vapour continuum region between 4-14μm (2500-714cm). Protonated water clusters are a common species of atmospheric molecular cluster-ion, produced by cosmic rays throughout the troposphere and stratosphere. Under clearsky conditions or periods of increased atmospheric ionisation, such as solar proton events, the IR absorption by atmospheric ions may affect climate through the radiative balance. Fourier Transform Infrared Spectrometry in a long path cell, of path length 545m has been used to detect IR absorption by corona-generated positive molecular cluster-ions. The column concentration of ions in the laboratory spectroscopy experiment was estimated to be ~10 m; the column concentration of protonated ∗ Corresponding author: email [email protected]