The gas-phase formation and spectroscopic characteristics of ethanimine have been re-investigated as a paradigmatic case illustrating the accuracy of state-of-the-art quantum-chemical (QC) methodologies in the field of astrochemistry. According to our computations, the reaction between the amidogen, NH, and ethyl, C2H5, radicals is very fast, close to the gas-kinetics limit. Although the main reaction channel under conditions typical of the interstellar medium leads to methanimine and the methyl radical, the predicted amount of the two E,Z stereoisomers of ethanimine is around 10%. State-of-the-art QC and kinetic models lead to a [E−CH3CHNH]/[Z−CH3CHNH] ratio of ca. 1.4, slightly higher than the previous computations, but still far from the value determined from astronomical observations (ca. 3). An accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers of ethanimine combined with millimeter-wave measurements up to 300 GHz, allows for predicting the rotational spectrum of both isomers up to 500 GHz, thus opening the way toward new astronomical observations.
Here we report the first theoretical characterization of the interface between the CuGaO
2
delafossite oxide and the carboxylic (–COOH) and phosphonic acid (–PO
3
H
2
) anchoring groups. The promising use of delafossites as effective alternative to nickel oxide in p-type DSSC is still limited by practical difficulties in sensitizing the delafossite surface. Thus, this work provides atomistic insights on the structure and energetics of all the possible interactions between the anchoring functional groups and the CuGaO
2
surface species, including the effects of the Mg doping and of the solvent medium. Our results highlight the presence of a strong selectivity toward the monodentate binding mode on surface Ga atoms for both the carboxylic and phosphonic acid groups. Since the binding modes have a strong influence on the hole injection thermodynamics, these findings have direct implications for further development of delafossite based p-type DSSCs.
The isomerization
of hydrogen cyanide to hydrogen isocyanide on
icy grain surfaces is investigated by an accurate composite method
(jun-Cheap) rooted in the coupled cluster ansatz and by density functional
approaches. After benchmarking density functional predictions of both
geometries and reaction energies against jun-Cheap results for the
relatively small model system HCN···(H
2
O)
2
, the best performing DFT methods are selected. A large cluster
containing 20 water molecules is then employed within a QM/QM′
approach to include a realistic environment mimicking the surface
of icy grains. Our results indicate that four water molecules are
directly involved in a proton relay mechanism, which strongly reduces
the activation energy with respect to the direct hydrogen transfer
occurring in the isolated molecule. Further extension of the size
of the cluster up to 192 water molecules in the framework of a three-layer
QM/QM′/MM model has a negligible effect on the energy barrier
ruling the isomerization. Computation of reaction rates by the transition
state theory indicates that on icy surfaces, the isomerization of
HNC to HCN could occur quite easily even at low temperatures thanks
to the reduced activation energy that can be effectively overcome
by tunneling.
The isomerization of hydrogen cyanide to hydrogen isocyanide on icy grain surfaces is investigated by an accurate composite method (jun-Cheap) rooted in the coupled cluster ansatz and by density functional approaches. After benchmarking density functional predictions of both geometries and reaction energies against jun-Cheap resultsfor the relatively small model system HCN•••(H 2 O) 2 the best performing DFT methods are selected. A large cluster containing 20 water molecules is then employed within a QM/QM approach to include a realistic environment mimicking the surface of icy grains. Our results indicate that four water molecules are directly involved in a proton relay mechanism, which strongly reduces the activation energy with respect to the direct hydrogen transfer occurring in the isolated molecule. Further extension of the size of the cluster up to 192 water molecules in the framework of a three-layer QM/QM /MM model has a negligible effect on the energy barrier ruling the isomerization. Computation of reaction rates by transition state theory indicates that on
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