A gas-phase nitrogen-nitrogen noncovalent interaction has been unveiled in the nitroethane-trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C-H⋅⋅⋅O and C-H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination.
By combining rotational spectroscopyinsupersonic expansion with the capability of state-of-the-art quantumchemical computations in accurately determining structural and energetic properties,the genuine nature of as ulfur-sulfur chalcogen bond between dimethyl sulfide and sulfur dioxide has been unveiled in agas-jet environment free from collision, solvent and matrix perturbations.ASAPT analysis pointed out that electrostatic S···S interactions play the dominant role in determining the stability of the complex, largely overcoming dispersion and CÀH···O hydrogen-bond contributions.Indeed, in agreement with the analysis of the quadrupole-coupling constants and of the methyl internal rotation barrier,the NBO and NOCV/CD approaches show am arked charge transfer between the sulfur atoms.B ased on the assignment of the rotational spectra for 7i sotopologues,a na ccurate semiexperimental equilibrium structure for the heavy-atom backbone of the molecular complex has been determined, whichis characterized by aS ···S distance (2.947(3) )w ell belowt he sum of van der Waals radii.
The 1:1 complex of ammonia with pyridine is characterized by using state-of-the-art quantum-chemical computations combined with pulsed-jet Fourier-transform microwave spectroscopy. The computed potential energy landscape indicates the formation of a stable σ-type complex, which is confirmed experimentally: analysis of the rotational spectrum shows the presence of only one 1:1 pyridine-ammonia adduct. Each rotational transition is split into several components owing to the internal rotation of NH around its C axis and to the hyperfine structure of both N quadrupolar nuclei, thus providing unequivocal proof that the two molecules form a σ-type complex involving both a N-H⋅⋅⋅N and a C-H⋅⋅⋅N hydrogen bond. The dissociation energy (BSSE- and ZPE-corrected) is estimated to be 11.5 kJ mol . This work represents the first application of an accurate yet efficient computational scheme, designed for the investigation of small biomolecules, to a molecular cluster.
This%is%the%final%accepted%manuscript%of:% % A.% Melli,% M.% Melosso,% N.% Tasinato,% et% al.% ROTATIONAL% AND% INFRARED% SPECTROSCOPY% OF% ETHANIMINE:%A%ROUTE%TOWARDS%ITS%ASTROPHYSICAL%AND%PLANETARY%DETECTION.%Astrophys.%J.% 855,%123%(2018);%DOI:%10.3847/1538U4357/aaa899% % Available%at:%https://doi.org/10.3847/1538U4357/aaa899% % ABSTRACTEthanimine, a possible precursor of amino acids, is considered an important prebiotic molecule and thus may play important roles in the formation of biological building-blocks in the interstellar medium. In addition, its identification in Titan's atmosphere would be important for understanding the abiotic synthesis of organic species. An accurate computational characterization of the molecular structure, energetics and spectroscopic properties of the E and Z isomers of ethanimine, CH 3 CHNH, has been carried out by means of a composite scheme based on coupled-cluster techniques, which also accounts for extrapolation to the complete basis-set limit and core-valence correlation correction, combined with density functional theory for the treatment of vibrational anharmonic e↵ects. By combining the computational results with new millimeter-wave measurements up to 300 GHz, the rotational spectrum of both isomers can be accurately predicted up to 500 GHz. Furthermore, our computations allowed us to revise the infrared spectrum of both E -and Z -CH 3 CHNH, thus predicting all fundamental bands with high accuracy.
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