Context.
The UV photoreactivity of polycyclic aromatic hydrocarbons (PAHs) in porous amorphous solid water has long been known to form both oxygenated photoproducts and photofragments.
Aims.
The aim ...of this study is to examine the influence of ice structure on reactivity under soft UV irradiation conditions.
Methods.
Mixtures of PAHs with amorphous solid water (porous and compact) and crystalline (cubic and hexagonal) ices were prepared in a high vacuum chamber and irradiated using a mercury lamp for up to 2.5 h.
Results.
The results show that the production of oxygenated PAHs is efficient only in amorphous water ice, while fragmentation can occur in both amorphous and crystalline ices. We conclude that the reactivity is driven by PAH–water interactions in favourable geometries, notably where dangling bonds are available at the surface of pores.
Conclusions.
These results suggest that the formation of oxygenated PAH molecules is most likely to occur in interstellar environments with porous (or compact) amorphous solid water and that this reactivity could considerably influence the inventory of aromatics in meteorites.
The photochemistry of ices with polycyclic aromatic hydrocarbons (PAHs) has been extensively studied, but to date no investigation has been made of PAHs in interaction with low numbers (n< 4) of ...molecules of water. We performed photochemical matrix isolation studies of coronene:water complexes, probing the argon matrix with FTIR spectroscopy. We find that coronene readily reacts with water upon irradiation with a mercury vapour lamp to produce oxygenated PAH photoproducts, and we postulate a reaction mechanism via a charge transfer Rydberg state. This result suggests that oxygenated PAHs should be widely observed in regions of the ISM with sufficiently high water abundances, for example near the edges of molecular clouds where water molecules begin to form, but before icy layers are observed, that is at AV< 3. In order to explain the low derived observational abundances of oxygenated PAHs, additional destruction routes must be invoked.
In this paper, we report a combined theoretical and experimental study of coronene:water interactions in low temperature argon matrices. The theoretical calculations were performed using the mixed ...density functional-based tight binding/force field approach. The results are discussed in the light of experimental matrix isolation FTIR spectroscopic data. We show that, in the solid phase, (C
H
)(H
O)
(n ≤ 6) σ-type complexes, i.e. with water molecules coordinated on the edge of coronene, are formed, whereas in the gas phase, π-interaction is preferred. These σ-complexes are characterised by small shifts in water absorption bands and a larger blue shift of the out-of-plane γ(CH) deformation of coronene, with the shift increasing with the number of complexed water molecules. Such σ interaction is expected to favour photochemical reaction between water and coronene at the edges of the coronene molecule, leading to the formation of oxidation products at low temperature, even in the presence of only a few water molecules and at radiation energies below the ionisation potential of coronene.
The complexation of β-cyclodextrin with monolayers of cholesterol, DMPC, DMPG, and mixtures of those lipids has been studied using Brewster microscopy, PMIRRAS, and ab initio calculations. An ...oriented channel-like structure of β-cyclodextrin, perpendicular to the air/water interface, was observed when some cholesterol molecules were present at the interface. This channel structure formation is the first step in the cholesterol dissolution in the subphase. With pure DMPC and DMPG monolayers, weaker, less organized complexes are formed, but they disappear almost completely at high surface pressure, and only a small amount of phospholipid is dissolved in the subphase.
This paper collects the results obtained in different studies on the interaction of the CO
2 molecule with transition metal atoms, using matrix isolation FTIR spectroscopy and density functional ...theory (DFT). Late-transition metal atoms (Fe, Co, Ni and Cu) form one-to-one M(CO
2) complexes, while those from the left-hand side in the periodic table (Ti, V, and Cr) insert spontaneously into a CO bond yielding oxocarbonyl species. Owing to isotopic experiments with
13CO
2 and C
18O
2, these results allow spectroscopic identification of carbon dioxide bonding modes in organometallic species containing CO
2 moiety. Special attention is paid to the interaction of CO
2 molecule with Ni and Ti atoms. In neat CO
2 matrices, it is shown that CO
2 is side-on coordinated to nickel in a 1:1 complex. The binding energy is weak (18 kcal mol
−1). In argon diluted matrices, no reaction occurs, even after annealing. Interestingly, the coordination of CO
2 is promoted by adding N
2 in the rare gas matrix. This is rationalized by comparing the potential energy curves corresponding to the interaction of the Ni atom or the NiN
2 moiety with CO
2. The binding energy is then 32 kcal mol
−1. DFT calculations show that Ti inserts with no energy barrier into a CO bond, resulting in an OTiCO insertion product, which is far more stable than any of the possible Ti(CO
2) complexes and reactive towards CO
2. An intrinsic reaction path for the insertion process is investigated.
In this paper, we report a combined theoretical and experimental study of coronene:water interactions in low temperature argon matrices. The theoretical calculations were performed using the mixed ...density functional-based tight binding/force field approach. The results are discussed in the light of experimental matrix isolation FTIR spectroscopic data. We show that, in the solid phase, (C
24
H
12
)(H
2
O)
n
(
n
≤ 6) σ-type complexes,
i.e.
with water molecules coordinated on the edge of coronene, are formed, whereas in the gas phase, π-interaction is preferred. These σ-complexes are characterised by small shifts in water absorption bands and a larger blue shift of the out-of-plane
γ
(CH) deformation of coronene, with the shift increasing with the number of complexed water molecules. Such σ interaction is expected to favour photochemical reaction between water and coronene at the edges of the coronene molecule, leading to the formation of oxidation products at low temperature, even in the presence of only a few water molecules and at radiation energies below the ionisation potential of coronene.
Coronene preferentially forms σ-type rather than π-type complexes with water in low temperature argon matrices.
Thanks to infrared thermography, we have studied the mechanisms of CO2 capture by solid adsorbents (CO2 capture via gas adsorption on various types of porous substrates) to better understand the ...physico-chemical mechanisms that control CO2-surface interactions. In order to develop in the future an efficient process for post-combustion CO2 capture, it is necessary to quantify the energy of adsorption of the gas on the adsorbent (exothermic process). The released heat (heat of adsorption) is a key parameter for the choice of materials and for the design of capture processes. Infrared thermography is used, at first approach, to detect the temperature fields on a thin-layer of adsorbent during CO2 adsorption. An analytical heat transfer model was developed to evaluate the adsorption heat flux and to estimate, via an inverse technique, the heat of adsorption. The main originality of our method is to estimate heat losses directly from the heat generated during the adsorption process. Then, the estimated heat loss is taken for an a posteriori calculation of the adsorption heat flux. Finally, the heat of adsorption may be estimated. The interest in using infrared thermography is also its ability to quickly change the experimental setup, for example, to switch from the adsorbent thin-layer to the adsorbent bed configuration. We present the first results tempting to link the thin-layer data to the propagation speed of the thermal front in a millifluidics adsorption bed, also observed by IR thermography.
The interaction of the CO2 molecule with nickel atoms was studied by using matrix isolation spectroscopy and density functional theory. In argon dilute matrices, no reaction occurs, even after ...annealing the deposit. In neat CO2 matrices, it is shown that carbon dioxide forms a 1:1 complex with nickel which is characterized by its UV−visible and FTIR absorptions, including isotopically labeled species. Theory predicts the side-on coordination mode to be the most stable. The binding energy of the side-on Ni(CO2) complex is estimated to be 18 kcal/mol. The calculated OCO angle is 145°, which is quite a large value compared to those encountered in other known CO2 complexes. In dinitrogen matrices, the yield of CO2 complexation is considerably enhanced relative to that in argon dilute and neat CO2 matrices, which is attributed to the formation of unsaturated Ni(N2) n complexes prior to CO2 coordination. The CO2 binding energies calculated for the Ni(CO2)(N2) n (n = 1, 2) complexes (respectively 32 and 4 kcal/mol) suggest that CO2 probably coordinates to the Ni(N2) complex. This is a very interesting result, owing to the fact that CO2 does not react with nickel atoms in dilute argon matrices.
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