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The characterization of the seleno-sulfide-bromo systems and the isomerization process on the [H, S, Se, Br] potential energy surface were investigated using state-of-the-art theoretical methods. The CCSD(T) and the MP2 levels of theory were employed along with the series of correlation consistent basis sets extrapolated to the complete basis set (CBS) limit in the optimization of the geometrical parameters and computation of electronic energies. The relative stability, in kcal mol, at the CCSD(T)/CBS follows the trend: HSSeBr (0) > HSeSBr (9.51) > SSeHBr (24.02) > SeSHBr (25.42). This order was observed in the previous study of the [H, S, Se, Cl] species. The structural parameters and vibrational frequencies of the [H, S, Se, Br] species are reported. This research work should be helpful to experimentalists in order to gain insights into these novel heteroatom molecules. [ABSTRACT FROM AUTHOR]

The optimized molecular structures, vibrational wavenumbers and corresponding vibrational assignments of the syn and anti conformers of 2-, 3- and 4-pyridine carboxaldehydes and their sulfur and selenium analogues were calculated using the density functional theory method employing the B3LYP functional with the 6-311++G(d,p) basis set and second order Møller-Plesset Perturbation Theory (MP2) method with the cc-pVDZ basis set. The calculations were adapted to the C symmetries of all ground state structures. The transition state arising from syn-anti isomerization was also modelled. All structures were fully optimized, and the geometries, rotational constants, dipole moments, charges, thermodynamic properties and energies are reported. Energies of the optimized structures were used to obtain the energy difference between the syn and anti conformers and the rotational barrier. The calculated vibrational wavenumbers were appropriately assigned to the various fundamental modes of vibrations. The Integral Equation Formalism Polarization Continuum Model was used to calculate the optimized geometry and the vibrational wavenumbers for all of the compounds in nine solvents: heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide and water. In addition, the LUMO, HOMO and energy band gap are also reported. The results indicate that the anti conformer is preferred with a rotational barrier of at least 19 kJ·mol. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The interstellar medium has a rich chemistry which involves a wide variety of molecules. Of particular interest are molecules that have a link to prebiotic chemistry which hold the key to understanding of our origins. On the basis of suggestions that selenium may have been involved in the origin and evolution of life, we have studied the selenium analogue of cyanoethenethiol, namely the novel cyanoetheneselenol. Cyanoetheneselenol exhibits conformational and geometrical isomerism. This theoretical work deals with the study of four forms of cyanoetheneselenol in terms of their structural, spectroscopic and thermodynamic parameters. All computations were performed using density functional theory method with the B3LYP functional and the Pople basis set, 6-311 + G(d,p), for all atoms. The relative stability of the four isomers of cyanoetheneselenol was obtained and interpreted. The infrared spectra were generated and assignment of the normal modes of vibration was performed. Probable regions of detection, proposed on the basis of parameters obtained from this study for the four isomers, include comets, the molecular cloud: Sagittarius B2(N), and planetary atmospheres. The molecular and spectroscopic parameters should be useful for future identification of the astrobiological molecule cyanoetheneselenol and the development of the Square Kilometre Array. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]