School of Chemistry University of Nottingham Laboratory Infrared Studies of Interstellar Ices Mark Collings School of Chemistry University of Nottingham Astrochemistry From Laboratory to Telescope Astrochemistry From Laboratory to Telescope Cardiff - 6 th January Cardiff - 6 th January 2005.

School of Chemistry University of Nottingham Observations of Interstellar Ices Figure reproduced from Whittet et.al. 1996, A&A, 315, L357.

School of Chemistry University of Nottingham Ice Mantles on Interstellar Dust Grains

School of Chemistry University of Nottingham RAIR Spectra of CO / H 2 O Mixture CO and H 2 O are co-deposited at 8 K, to give a film of ~ 5 % CO.CO and H 2 O are co-deposited at 8 K, to give a film of ~ 5 % CO. Spectra are recorded in reflection-absorption infrared configuration.Spectra are recorded in reflection-absorption infrared configuration. The film is annealed then cooled to the base temperature (8 K) before the IR scan is recorded. Therefore all observed changes are irreversible.The film is annealed then cooled to the base temperature (8 K) before the IR scan is recorded. Therefore all observed changes are irreversible.

School of Chemistry University of Nottingham Ballistic CO Deposition H 2 O film deposited at varying temperature.H 2 O film deposited at varying temperature. CO deposited at 8 K – ballistic adsorption; i.e. “stick and stop”.CO deposited at 8 K – ballistic adsorption; i.e. “stick and stop”. Roughly half the “surface” covered in each case.Roughly half the “surface” covered in each case. Adsorbed CO samples surface sites in a statistical ratio.Adsorbed CO samples surface sites in a statistical ratio.

School of Chemistry University of Nottingham CO Deposition at Elevated Temperature CO adsorbed at 30 K, at which temperature CO molecules are able to diffuse across the water ice surface.CO adsorbed at 30 K, at which temperature CO molecules are able to diffuse across the water ice surface. CO adsorbed at the strongest adsorption sites first.CO adsorbed at the strongest adsorption sites first.

School of Chemistry University of Nottingham CO Saturation of Varying Ice Surfaces CO deposition at 30 K continued until the surface is saturated.CO deposition at 30 K continued until the surface is saturated. Ratio of peaks changes for CO adsorption on porous ices.Ratio of peaks changes for CO adsorption on porous ices. High frequency peak shifts to lower wavenumberHigh frequency peak shifts to lower wavenumber

School of Chemistry University of Nottingham Difference Spectra – CO/H 2 O Mixture Spectra from the set shown previously.Spectra from the set shown previously.

School of Chemistry University of Nottingham Difference Spectra – CO/H 2 O Mixture Spectra from the set shown previously.Spectra from the set shown previously. Difference spectrum highlights the changes.Difference spectrum highlights the changes.

School of Chemistry University of Nottingham Difference Spectra – Saturated CO Adsorption Difference spectrum between saturated monolayer and sub- monolayer (i.e. unsaturated monolayer).Difference spectrum between saturated monolayer and sub- monolayer (i.e. unsaturated monolayer).

School of Chemistry University of Nottingham Difference Spectra – Multilayer Difference spectrum between multilayer and sub-monolayer where CO adsorption is ballistic.Difference spectrum between multilayer and sub-monolayer where CO adsorption is ballistic.

School of Chemistry University of Nottingham Difference Spectra – Multilayer on Crystalline Ice I c Water ice deposited at 140 K to give a cubic crystalline structure.Water ice deposited at 140 K to give a cubic crystalline structure. The ice surface is as ordered as we can make it.The ice surface is as ordered as we can make it.

School of Chemistry University of Nottingham The CO Stretch Absorption in Observational Spectra Figure reproduced from Pontoppidan et.al. 2003, A&A, 408, 981.

School of Chemistry University of Nottingham Evolution of Layered CO-H 2 O Ice Figure reproduced from Fraser et.al. 2004, MNRAS, 353, 59.

School of Chemistry University of Nottingham RAIR Spectrum of Pure CO CO stretch observed at 2139 cm -1 in astronomical spectra and laboratory transmission experiments - transverse optical (TO) mode.CO stretch observed at 2139 cm -1 in astronomical spectra and laboratory transmission experiments - transverse optical (TO) mode. CO stretch observed at 2142 cm -1 in RAIRS experiments – longitudinal optical (LO) mode.CO stretch observed at 2142 cm -1 in RAIRS experiments – longitudinal optical (LO) mode.

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham N 2 Deposition

School of Chemistry University of Nottingham CO Adsorption on N 2 Films

School of Chemistry University of NottinghamConclusions IR spectroscopy of CO is an ideal probe of the structure of water ice, an important consideration when studying chemistry occurring within water films.IR spectroscopy of CO is an ideal probe of the structure of water ice, an important consideration when studying chemistry occurring within water films. Laboratory experiments indicate that water ice on interstellar dust grains is porous, but that the sites that give rise to the 2152 cm -1 CO stretch feature are blocked.Laboratory experiments indicate that water ice on interstellar dust grains is porous, but that the sites that give rise to the 2152 cm -1 CO stretch feature are blocked. The optical properties of an underlying film can influence the position and size of observed bands in an overlayer of CO.The optical properties of an underlying film can influence the position and size of observed bands in an overlayer of CO.

School of Chemistry University of NottinghamAcknowledgements Martin McCoustra, John DeverMartin McCoustra, John Dever University of Nottingham Helen FraserHelen Fraser University of Strathclyde Elisabetta Palumbo, Giuseppe BarattaElisabetta Palumbo, Giuseppe Baratta Catania Astrophysical Observatory Funding byFunding by &