Theoretical characterization of the SiC3H- anion

Theoretical characterization of C7, C7-, and C7+

We present a theoretical investigation of neutral and ionic C7 molecules. Since carbon chains present isomerism and the number of possible structures increases fast with the number of carbon atoms, a B3LYP∕aug-cc-pVTZ search of stationary points has been achieved. For C7, we found twelve minimal structures. Among these forms, eleven C7 isomers are located into the lowest singlet hyper potential energy surface. The most stable form of C7 is linear and possesses a (1)Σg(+) symmetry species. For C7(-), we characterized fifteen stable forms, where twelve are of doublet spin-multiplicity. The global minimum of C7(-) is a (2)Πg doubly degenerate Renner-Teller structure. For C7(+) cation, we found eleven doublet and three quartet isomers with a 7-atom cycle, C7(+) (X(2)A1) ground state. For the most stable forms, explicitly correlated (R)CCSD(T)-F12 calculations have been performed for the determination of equilibrium geometries and for the spectroscopic characterization of C7, C7(-), and C7(+), providing accurate rotational constants and harmonic frequencies. Vertical excitation energies to the lowest electronic states have been computed at the CASSCF∕MRCI∕aug-cc-pVTZ level. Thirty five electronic states of C7, suitable of being involved in reactive processes, lie below 7 eV. Fourteen metastable electronic states of C7(-) have been found below 3.5 eV. For linear-C7, we compute the electron affinity and the ionization energy to be 3.38 eV and 10.42 eV, respectively.

Highly correlated ab initio study of the low frequency modes of propane and various monosubstituted isotopologues containing D and 13C

With the purpose of providing some clues that could encourage the spectral recordings of propane and various monodeuterated and (13)C isotopologues and also to explore their far infrared spectra at low temperatures, the energy levels corresponding to their three lowest frequency modes are determined variationally using a flexible model in three dimensions. Five vibrationally corrected potential energy surfaces are computed using CCSD(T) ab initio calculations. In spite of the quality of these highly correlated potentials in molecules with similar structures, it was proven that an empirical adjustment of the surfaces would enclose accurately the experimental and theoretical frequency residuals and therefore it is also used in the present work. Interacting terms, energy levels and tunneling splittings are provided for CH3CH2CH3, CH3(13)CH2CH3, (13)CH3CH2CH3, CH2DCH2CH3 and CH3CHDCH3. Infrared and Raman transitions of CH3CH2CH3 are assigned. Correlation between symmetry species of the five isotopologue symmetry groups (G36, G36, G18, G6 and G'18, respectively) is established for the classification of the levels and torsional splittings. The rotational constants are determined with CCSD(T)/CBS (A0 = 29263.46 MHz, B0 = 8454.10 MHz and C0 = 7466.64 MHz) using a non-relativistic procedure. Fundamental anharmonic frequencies corresponding to the high and medium amplitude modes are computed for all the isotopologues. The adjusted parameters are accurate enough to be employed in further spectral analysis.