RESUMEN
The reaction system between the simplest Criegee intermediate, CH2OO, and the greenhouse gas CO2 has been investigated by Fourier transform microwave spectroscopy. The CH2OO-CO2 weakly bound complex was identified in the rotational spectrum, where inversion doublets due to the tunnelling motion between two equivalent configurations of the complex, with CO2 located at one side or the other side of the CH2OO plane, were observed. Using a two-state torsion-rotation Hamiltonian, a complete set of rotational and centrifugal distortion constants for both tunneling states were derived. In addition, the torsional energy difference between both states could be accurately determined, being 23.9687 MHz. The non-observation of the cycloaddition reaction product is in agreement with our ab initio calculations and with previous results that concluded that the reactivity of CIs toward CO2 is measured to be quite limited.
RESUMEN
We investigate the performance of a set of recently introduced range-separated double-hybrid functionals, namely ωB2-PLYP, ωB2GP-PLYP, RSX-0DH, and RSX-QIDH models for hard-to-calculate excitation energies. We compare with the parent (B2-PLYP, B2GP-PLYP, PBE0-DH, and PBE-QIDH) and other (DSD-PBEP86) double-hybrid models as well as with some of the most widely employed hybrid functionals (B3LYP, PBE0, M06-2X, and ωB97X). For this purpose, we select a number of medium-sized intra- and inter-molecular charge-transfer excitations, which are known to be challenging to calculate using time-dependent density-functional theory (TD-DFT) and for which accurate reference values are available. We assess whether the high accuracy shown by the newest double-hybrid models is also confirmed for those cases too. We find that asymptotically corrected double-hybrid models yield a superior performance, especially for the inter-molecular charge-transfer excitation energies, as compared to standard double-hybrid models. Overall, the PBE-QIDH and its corresponding range-separated RSX-QIDH functional are recommended for general-purpose TD-DFT applications, depending on whether long-range effects are expected to play a significant role.
RESUMEN
Fluorinated derivatives of biological molecules have proven to be highly efficient at modifying the biological activity of a given protein through changes in the stability and the kind of docking interactions. These interactions can be hindered or facilitated based on the hydrophilic/hydrophobic character of a particular protein region. Diadamantyl ether (C20 H30 O) possesses both kinds of docking sites, serving as a good template to model these important contacts with aromatic fluorinated counterparts. In this work, an experimental study on the structures of several complexes between diadamantyl ether and benzene as well as a series of fluorinated benzenes is reported to analyze the effect of HâF substitution on the interaction and structure of the resulting molecular clusters using rotational spectroscopy. All experimentally observed complexes are largely dominated by London dispersion interactions with the hydrogen-terminated surface areas of diadamantyl ether. Already single substitution of one hydrogen atom with fluorine changes the preferred docking site of the complexes. However, the overall contributions of the different intermolecular interactions are similar for the different complexes, contrary to previous studies focusing on the difference in interactions using fluorinated and non-fluorinated molecules.
RESUMEN
Ice and solid H2 S look as different as pears and oranges, leading Pauling to conclude that H2 O has hydrogen bonds and H2 S has van der Waals interactions. Now it is shown that the H2 S dimer, like the H2 O dimer, is indeed hydrogen-bonded.