Adsorption and Desorption of Mixed Ices Cosmic Dust Adsorption and Desorption of Mixed Ices

Experimental Aims Investigate the formation of methanol on dust grain surfaces Study the desorption characteristics of mixed ices using TPD Initially study methanol on a pre-dose of water ice Vary the pre-dose of water to study: Methanol on a thin layer of Water Ice Methanol on a thick layer of Water Ice

Experimental Set-up UHV chamber with facilities to cool the sample to 10 – 20 K, coupled to an atom source Mimic conditions in ISM Reflection Absorption Infrared Spectroscopy (RAIRS) and Temperature Programmed Desorption (TPD) studies

Temperature Programmed Desorption Heat sample in a linear manner Monitor desorbing species with a QMS Adsorption kinetics can be determined by analysing the spectra.

Methanol on Single Layer Ice

Water Spectra: Single Layer

Methanol on Single Layer: Summary Layer of low density amorphous ice forms Monolayer of methanol on the water layer Multilayer methanol formation

Methanol on Thick Layer Ice

Water Spectra: Thick Layer

Methanol on Thick Layer Summary Thick layer of low density amorphous ice Methanol binds to pores in ice surface – dependent on ice thickness Monolayer of methanol on the water layer Multilayer methanol formation

Summary of Mixed Ice Features Methanol shows complex desorption features highlighting need for mixed ice studies Co-desorption feature possibly indicating trapping. Intensity dependent on thickness of water layer Monolayer on ice Multilayer Heavily influenced by H-bonding Methanol to H2O interaction > methanol to methanol

Future work Analyse results Repeat TPD with methanol and water co-adsorbed Vary proportions of the mixture RAIRS

Acknowledgements Deep Bolina, Sabine Barjansky, Carolina Carlstedt Wendy Brown UCL Centre for Cosmic Chemistry and Physics EPSRC Royal Society