The adsorption and desorption of ethanol ices from a model grain surface

Reversible solvent interactions with UiO-67 metal-organic frameworks

The utility of UiO-67 Metal-Organic Frameworks (MOFs) for practical applications requires a comprehensive understanding of intermolecular host-guest MOF-analyte interactions. To investigate intermolecular interactions between UiO-67 MOFs and complex molecules, it is useful to evaluate the interactions with simple polar and non-polar analytes. This problem is approached by investigating the interactions of polar (acetone and isopropanol) and non-polar (n-heptane) molecules with functionalized UiO-67 MOFs via temperature programmed desorption mass spectrometry and temperature programmed Fourier transform infrared spectroscopy. We find that isopropanol, acetone, and n-heptane bind reversibly and non-destructively to UiO-67 MOFs, where MOF and analyte functionality influence relative binding strengths (n-heptane ≈ isopropanol > acetone). During heating, all three analytes diffuse into the internal pore environment and directly interact with the μ3-OH groups located within the tetrahedral pores, evidenced by the IR response of ν(μ3-OH). We observe nonlinear changes in the infrared cross sections of the ν(CH) modes of acetone, isopropanol, and n-heptane following diffusion into UiO-67. Similarly, acetone's ν(C=O) infrared cross section increases dramatically when diffused into UiO-67. Ultimately, this in situ investigation provides insights into how individual molecular functional groups interact with UiO MOFs and enables a foundation where MOF interactions with complex molecular systems can be evaluated.

Low Temperature Multilayer Adsorption of Methanol and Ethanol on Platinum

Adsorption of methanol and ethanol on the clean Pt (111) surface was studied at temperatures between 80 and 130 K using polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS). It was shown that adsorption of methanol at 80 K leads to the formation of amorphous solid methanol, and fast crystallization of the amorphous phase occurs upon warming at 100 K. Vapor deposition of methanol at 100 K directly leads to the formation of well-crystallized layers of solid methanol. According to PM-IRRAS, these crystalline layers consist of chains of hydrogen-bonded methanol molecules lying in a plane oriented close to the normal to the platinum surface. Adsorbed methanol is removed completely from platinum after heating to 120 K. Vapor deposition of ethanol at 80 K also leads to the formation of amorphous solid ethanol. However, subsequent warming does not lead to ordering of the adsorption layers, and at 130 K, ethanol is also completely desorbed.

Using Surface Science Techniques to Investigate the Interaction of Acetonitrile with Dust Grain Analogue Surfaces : Behaviour of acetonitrile and water on a graphitic surface

Surface science methodologies, such as reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD), are ideally suited to studying the interaction of molecules with model astrophysical surfaces. Here we describe the use of RAIRS and TPD to investigate the adsorption, interactions and thermal processing of acetonitrile and water containing model ices grown under astrophysical conditions on a graphitic dust grain analogue surface. Experiments show that acetonitrile physisorbs on the graphitic surface at all exposures. At the lowest coverages, repulsions between the molecules lead to a decreasing desorption energy with increasing coverage. Analysis of TPD data gives monolayer desorption energies ranging from 28.8‐39.2 kJ mol−1 and an average multilayer desorption energy of 43.8 kJ mol−1. When acetonitrile is adsorbed in the presence of water ice, the desorption energy of monolayer acetonitrile shows evidence of desorption with a wide range of energies. An estimate of the desorption energy of acetonitrile from crystalline ice (CI) shows that it is increased to ~37 kJ mol−1 at the lowest exposures of acetonitrile. Amorphous water ice also traps acetonitrile on the graphite surface past its natural desorption temperature, leading to volcano and co-desorption. RAIRS data show that the C≡N vibration shifts, indicative of an interaction between the acetonitrile and the water ice surface.

Ethanol-ethylene conversion mechanism on hydrogen boride sheets probed by in situ infrared absorption spectroscopy

Two-dimensional hydrogen boride (HB) sheets were recently demonstrated to act as a solid acid catalyst in their hydrogen-deficient state. However, both the active sites and the mechanism of the catalytic process require further elucidation. In this study, we analyzed the conversion of ethanol adsorbed on HB sheets under vacuum during heating using in situ Fourier transform infrared (FT-IR) absorption spectroscopy with isotope labelling. Up to 450 K, the FT-IR peak associated with the OH group of the adsorbed ethanol molecule disappeared from the spectrum, which was attributed to a dehydration reaction with a hydrogen atom from the HB sheet, resulting in the formation of an ethyl species. At temperatures above 440 K, the number of BD bonds markedly increased in CD₃CH₂OH, compared to CH₃CD₂OH; the temperature dependence of the formation rate of BD bonds was similar to that of the dehydration reaction rate of ethanol on HB sheets under steady-state conditions. The rate-determining step of the dehydration of ethanol on HB was thus ascribed to the dehydrogenation of the methyl group of the ethyl species on the HB sheets, followed by the immediate desorption of ethylene. These results show that the catalytic ethanol dehydration process on HB involves the hydrogen atoms of the HB sheets. The obtained mechanistic insights are expected to promote the practical application of HB sheets as catalysts.

An IR investigation of solid amorphous ethanol - Spectra, properties, and phase changes

Mid- and far-infrared spectra of condensed ethanol (CH₃CH₂OH) at 10-160K are presented, with a special focus on amorphous ethanol, the form of greatest astrochemical interest, and with special attention given to changes at 155-160K. Infrared spectra of amorphous and crystalline forms are shown. The refractive index at 670nm of amorphous ethanol at 16K is reported, along with three IR band strengths and a density. A comparison is made to recent work on the isoelectronic compound ethanethiol (CH₃CH₂SH), and several astrochemical applications are suggested for future study.

Desorption and crystallisation of binary 2-propanol and water ices adsorbed on graphite

Strong interactions between 2-propanol and water ice cause marked changes in the crystallisation kinetics and desorption of water.

Physisorption and desorption of H2, HD and D2 on amorphous solid water ice. Effect on mixing isotopologue on statistical population of adsorption sites

We study the adsorption and desorption of three isotopologues of molecular hydrogen mixed on 10 ML of porous amorphous water ice (ASW) deposited at 10 K.