Showing papers by "Óscar Gálvez published in 2013"

On the mechanism of iodine oxide particle formation

Abstract: The formation of atmospherically relevant iodine oxides IxOy (x = 1,…,3, y = 1,…,7) has been studied experimentally using time-of-flight mass spectrometry combined with a soft ionisation source, complemented with ab initio electronic structure calculations of ionisation potentials and bond energies at a high level of theory presented in detail in the accompanying paper (Galvez et al., 2013). For the first time, direct experimental evidence of the I2Oy (y = 1,…,5) molecules in the gas phase has been obtained. These chemical species are observed alongside their precursors (IO and OIO) in experiments where large amounts of aerosol are also generated. The measured relative concentrations of the IxOy molecules and their dependence on ozone concentration have been investigated by using chemical modelling and rate theory calculations. It is concluded that I2O4 is the most plausible candidate to initiate nucleation, while the contribution of I2O5 in the initial steps is likely to be marginal. The absence of large I3Oy (y = 3,…,6) peaks in the mass spectra and the high stability of the I2O4–I2O4 dimer indicate that dimerisation of I2O4 is the key step in iodine oxide particle nucleation.

A theoretical study on the formation of iodine oxide aggregates and monohydrates

Abstract: Biotic and abiotic emissions of molecular iodine and iodocarbons from the sea or the ice surface and the intertidal zone to the coastal/polar marine boundary layer lead to the formation of iodine oxides, which subsequently nucleate forming iodine oxide particles (IOPs). Although the link between coastal iodine emissions and ultrafine aerosol bursts is well established, the details of the nucleation mechanism have not yet been elucidated. In this paper, results of a theoretical study of a range of potentially relevant aggregation reactions of different iodine oxides, as well as complexation with water molecules, are reported. Thermochemical properties of these reactions are obtained from high level ab initio correlated calculations including spin–orbit corrections. The results show that the nucleation path most likely proceeds through dimerisation of I2O4. It is also shown that water can hinder gas-to-particle conversion to some extent, although complexation with key iodine oxides does not remove enough of these to stop IOP formation. A consistent picture of this process emerges from the theoretical study presented here and the findings of a new laboratory study reported in the accompanying paper (Gomez Martin et al., 2013).

Optical constants of nh3 and nh3:n2 amorphous ices in the near-infrared and mid-infrared regions

Abstract: Ammonia ice has been detected on different astrophysical media ranging from interstellar medium (ISM) particles to the surface of various icy bodies of our solar system, where nitrogen is also present. We have carried out a detailed study of amorphous NH3 ice and NH3:N2 ice mixtures, based on infrared (IR) spectra in the mid-IR (MIR) and near-IR (NIR) regions, supported by theoretical quantum chemical calculations. Spectra of varying ice thicknesses were obtained and optical constants were calculated for amorphous NH3 at 15 K and 30 K and for a NH3:N2 mixture at 15 K over a 500-7000 cm–1 spectral range. These spectra have improved accuracy over previous data, where available. Moreover, we also obtained absolute values for the band strengths of the more prominent IR features in both spectral regions. Our results indicate that the estimated NH3 concentration in ISM ices should be scaled upward by ~30%.