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

2. 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

3. 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

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

5. Methanol on Single Layer Ice

6. Water Spectra: Single Layer

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

8. Methanol on Thick Layer Ice

9. Water Spectra: Thick Layer

10. 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

11. 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

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

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