Recent laboratory measurements have confirmed that chemical desorption (desorption of products due to exothermic surface reactions) can be an efficient process. The impact of including this process into gas-grain chemical models entirely depends on the formalism used and the associated parameters. Among these parameters, binding energies are probably the most uncertain ones for the moment. We propose a new model to compute binding energy of species to water ice surfaces. We have also compared the model results using either the new chemical desorption model proposed by Minissale et al. (2016) or the one of Garrod et al. (2007). The new binding energies have a strong impact on the formation of complex organic molecules. In addition, the new chemical desorption model from Minissale produces a much smaller desorption of these species and also of methanol. Combining the two effects, the abundances of CH 3 OH and COMs observed in cold cores cannot be reproduced by astrochemical models anymore.

The coupling of carbon dioxide (CO2) with epoxides with the formation of cyclic carbonates is a highly attractive 100% atom economic reaction. It represents a greener and safer alternative to the conventional synthesis of cyclic carbonates from diols and toxic phosgene.

We experimentally determined complete fallo † curves of the rate constant for the unimolecular decomposition of ethoxy radicals. Two di †erent techniques, laser Ñash photolysis and fast Ñow reactor were used both coupled to a detection of radicals by laser induced Ñuorescence. Experiments were performed at total C 2 H 5 Op ressures between 0.001 and 60 bar of helium and in the temperature range of 391È471 K. Under these conditions the b-CÈC scission (1a)is the dominating decompositionFrom a complete analysis of the experimental fallo † curves the low and the high pressure limiting rate constants of 3.3 ] 10~8 exp([58.5 kJ mol~1/RT ) cm3 s~1 and exp([70.3 kJ k 1a,0 \ [He] k 1a,= \ 1.1 ] 1013 mol~1/RT ) s~1 were extracted. We estimate an uncertainty for the absolute values of these rate constants of ^30%. Preexponential factor and activation energy are signiÐcantly lower than previous estimations. The rate constants are discussed in terms of statistical unimolecular rate theory. Excellent agreement between the experimental and the statistically calculated rate constants has been found. BAC-MP4, QCISD(T), or higher level of theory provide a reliable picture of the energy and the structure of the transition state of this radical bond dissociation reaction. On the same theoretical basis we predict the high pressure limiting rate constant for the b-CÈH scission (1b) of exp([84 kJ CH 3 CH 2 O~] M ] CH 3 CHO ] H~] M k 1b,= \ 1.3 ] 1013 mol~1/RT ) s~1. Atmospheric implications are discussed.

The electronic structure at organic/organic interfaces plays a key role, among others, in defining the quantum efficiency of organics-based photovoltaic cells. Here, we perform quantum-chemical and microelectrostatic calculations on molecular aggregates of various sizes and shapes to characterize the interfacial dipole moment at pentacene/C 60 heterojunctions. The results show that the interfacial dipole mostly originates in polarization effects due to the asymmetry in the multipolar expansion of the electronic density distribution between the interacting molecules, rather than in a charge transfer from donor to acceptor. The local dipole is found to fluctuate in sign and magnitude over the interface and appears as a sensitive probe of the relative arrangements of the pentacene and C 60 molecules (and of the resulting local electrical fields sensed by the molecular units).

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Abstract.Recent studies of neutral gas-phase reactions characterized by barriers show that certain complex forming processes involving light atoms are enhanced by quantum mechanical tunneling at low temperature. Here, we performed kinetic experiments on the activated C( 3 P) + H 2 O reaction, observing a surprising reactivity increase below 100 K, an effect which is only partially reproduced when water is replaced by its deuterated analogue. Product measurements of H-and D-atom formation allowed us to quantify the contribution of complex stabilization to the total rate while confirming the lower tunneling efficiency of deuterium. This result, which is validated through statistical calculations of the intermediate complexes and transition states has important consequences for simulated interstellar water abundances and suggests that tunneling mechanisms could be ubiquitous in cold dense clouds.Introduction.

We review the reactions between carbon chain molecules and radicals, namely C n , C n H, C n H 2 , C 2n+1 O, C n N, HC 2n+1 N, with C, N and O atoms. Rate constants and branching ratios for these processes have been re-evaluated using experimental and theoretical literature data. In total 8 new species have been introduced, 41 new reactions have been proposed and 122 rate coefficients from kida.uva.2011 ) have been modified. We test the effect of the new rate constants and branching ratios on the predictions of gas-grain chemical models for dark cloud conditions using two different C/O elemental ratios. We show that the new rate constants produce large differences in the predicted abundances of carbon chains since the formation of long chains is less effective. The general agreement between the model predictions and observed abundances in the dark cloud TMC-1 (CP) is improved by the new network and we find that C/O ratios of 0.7 and 0.95 both produce a similar agreement for different times. The general agreement for L134N (N) is not significantly changed. The current work specifically highlights the importance of O + C n H and N + C n H reactions. As there are very few experimental or theoretical data for the rate constants of these reactions we highlight the need for experimental studies of the O + C n H and N + C n H reactions, particularly at low temperature.

The addition of fluorinated alcohols to onium salts provides highly efficient organocatalysts for the chemical fixation of CO2 into epoxides under mild experimental conditions. The combination of online kinetic studies, NMR titrations and DFT calculations allows understanding this synergistic effect that provides an active organocatalyst for CO2 /epoxides coupling.