Adsorption and Thermal Processing of Glycolaldehyde, Methyl Formate, and Acetic Acid on Graphite at 20 K

Abstract

We present the first detailed comparative study of the adsorption and thermal processing of the three astrophysically important C2O2H4 isomers glycolaldehyde, methyl formate, and acetic acid adsorbed on a graphitic grain analogue at 20 K. The ability of the individual molecule to form intermolecular hydrogen bonds is extremely important, dictating the growth modes of the ice on the surface and the measured desorption energies. Methyl formate forms only weak intermolecular bonds and hence wets the graphite surface, forming monolayer, bilayer, and multilayer ices, with the multilayer having a desorption energy of 35 kJ mol(-1). In contrast, glycolaldehyde and acetic acid dewet the surface, forming clusters even at the very lowest coverages. The strength of the intermolecular hydrogen bonding for glycolaldehyde and acetic acid is reflected in their desorption energies (46.8 and 55 kJ mol(-1), respectively), which are comparable to those measured for other hydrogen-bonded species such as water. Infrared spectra show that all three isomers undergo structural changes as a result of thermal processing. In the case of acetic acid and glycolaldehyde, this can be assigned to the formation of well-ordered, crystalline, structures where the molecules form chains of hydrogen-bonded moieties. The data reported here are of relevance to astrochemical studies of hot cores and star-forming regions and can be used to model desorption from interstellar ices during the warm up phase with particular importance for complex organic molecules.

Trapping and desorption of complex organic molecules in water at 20 K

“…With this in mind, we present a detailed temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) study of the interactions of the C 2 O 2 H 4 isomers, glycolaldehyde, methyl formate, and acetic acid, adsorbed on and within amorphous solid water (ASW) and crystalline water (CI) ices grown on highly oriented pyrolytic graphite (HOPG) at ∼20 K. These isomers contain a range of functional groups that have varying strengths of intermolecular (within the pure ice) and intramolecular (with water) interactions. 8 As we show here, these interactions can influence the desorption behaviour of the isomers themselves, in addition to affecting the behaviour of the water ice.…”

“…5 As a result, there has been an increasing focus on the study of COMs in the laboratory. In particular, there have been investigations of the thermal processing of glycolaldehyde, methyl formate, and acetic acid [6][7][8] and studies of the molecular formation pathways of glycolaldehyde, [9][10][11] ethylene glycol, 11 and methyl formate, 12,13 amongst others. 14 The three isomers of C 2 O 2 H 4 (glycolaldehyde, methyl formate, and acetic acid) are an important group of COMs, given their classification as potential pre-biotic species.…”

Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts

“…The band of adsorbed methane shows an increasing trend during the reaction. There are also other peaks in these regions which are indexed to other compounds and were detected in very small amounts in GC-MS (as mentioned above): methyl formate (MF) 39,50,51 , ethyl methyl ether (EME) 52 , ethanol [53][54][55] , propane [56][57][58] and butane 59 . This can be the result of random formation in the gas phase rather than the catalyst's activity.…”

A fibre-coupled UHV-compatible variable angle reflection-absorption UV/visible spectrometer

“…Previous studies of molecular ices have used assumed values for n where experimental values are unavailable, or used values from the liquid phase. 9,10 Typical astrochemical surface science experiments employ high-vacuum (p ≈ 10 -7 mbar) 21,22 or ultra-high vacuum (UHV, p ≈ 10 -10 mbar) 7,23 and cryogenic cooling of the order of 10-30 K. [22][23][24] It is therefore questionable to assume that an ice will behave in the same way as in the liquid phase under ambient conditions. In other cases, when ices of mixed compositions were studied, a weighted average value based upon the relative contributions of each ice component was used for n. 15 However, this does not take into account interactions within the ice, and therefore the actual refractive index will vary significantly from that derived in this way.…”