Ab initiomolecular orbital study of structures and energetics of Si3H2, Si3H2+, and Si3H2−

Cyclopropenylidene: Clustering and Interaction with Water Molecules

Cyclopropenylidene (c-C₃H₂, abbreviated CPD) is a highly reactive, planar, partially aromatic carbene discovered in the interstellar medium, and, also recently, in the outer solar system. It is demonstrated herein on cogent quantum chemical grounds that CPD which possesses an electric dipole moment of 3.4 D is capable of forming stable dimer and trimer clusters through hydrogen-bonding. These attributes of CPD are conducive to the formation of stable hydrogen-bonded conformations with one- and two-water molecules. Having determined its consistency with the second-order Møller-Plesset perturbation theory MP2, we employ the ωB97xD hybrid density functional theory in conjunction with a 6-311++G(2d,2p) basis set for a credible description of noncovalent interactions involved in clustering. Molecular electrostatic potential (MESP) and characteristic vibrational frequency shifts upon clustering are presented.

Structures and transition states of Ge2CH2

In this study a systematic theoretical investigation of Ge2CH2 is carried out. The singlet potential energy surface (PES) was explored using state-of-the-art theoretical methods including self-consistent field (SCF), coupled cluster theory incorporating single and double excitation (CCSD), perturbative triple [CCSD(T)] and full triples [CCSDT] with perturbative quadruple (Q), together with a variety of correlation-consistent polarized valence basis sets cc-pVXZ (where X = D, T, and Q). A total of eleven stationary points have been located on the Ge2CH2 singlet ground state PES. Among them, seven structures are minima (1S-7S), two are transition states (TS1 and TS2), and two are second-order saddle points (SSP1 and SSP2). The global minimum is predicted to be an exotic hydrogen-bridged structure 1S. The energy ordering of the seven minima (in kcal mol(-1)) obtained from focal point analysis using the extrapolation to complete basis set (CBS) limit with zero point vibrational energy (ZPVE), core correlation, diagonal Born-Oppenheimer (DBOC) and relativistic correction is 1S [0.0] < 2S [17.2] < 3S [18.3] < 4S [31.7] < 5S [39.9] < 6S [58.1] < 7S [82.1].

Ab initiomolecular-orbital study of structures and energetics of Si3H3 neutral and anion

The geometric structures and isomeric stabilities of various stationary points in Si(3)H(3) neutral and its anion are investigated at the coupled-cluster singles, doubles (triples) [CCSD(T)] level of theory. For geometrical surveys, the basis sets used are of the Dunning's correlation consistent basis sets of triple-zeta quality for the neutral. To the anions, the Dunning's correlation consistent basis sets of double-zeta quality with diffuse functions are applied. For the three lower-lying anion isomers, the Dunning's correlation consistent basis sets of triple-zeta quality with diffuse functions (aug-cc-pVTZ) are also used. The final energies for the optimized stationary points are calculated at the CCSD(T) level of theory with the aug-cc-pVTZ basis sets. The basis sets of 6-311++G(3df,2pd) were also used for the lower-lying anion isomers. The Gaussian-2 method was performed only for the lower-lying anion isomers to clarify the relative stabilities. The global minimum neutral 1 (C(1):(2)A) has an unsymmetrical hydrogen-bridged bond; the conformer 2 in C(s) symmetry is a saddle point connecting the two equivalent isomers 1. Two lower-lying isomers (3 and 4) are also predicted within the energy range of 20 kJmol. In the anion, however, the conformer 4 (C(s):(1)A(')) with five formal valence electrons is a global minimum. Two more isomers (2 and 3) lie within 20 kJmol as in the neutral; the conformer 1 converts to the isomer 2. The quartets for the neutrals and diradical triplets for the anions were further studied; lower-lying quartets and triplets, competing with the corresponding doublet and singlet, respectively, were not found in the present systems. The vertical and adiabatic electron affinities of the global minimum neutral 1, producing the second lowest-lying anion isomer 2, amount to 2.18 and 2.35 eV, respectively, at the CCSD(T)/aug-cc-pVTZ level of theory. The electron addition to the third lowest-lying neutral isomer 4 produces the largest vertical electron affinities of 2.48 eV. The D(3h) structure, being the global minimum in the corresponding Si(3)H(3) (+) cation (trisilacyclopropenyl cation), converts to the isomer 8 (C(s)) or 11 (C(2)) due to the Jahn-Teller effect in the Si(3)H(3) neutral.

Theoretical study on isomeric stabilities of C2H2Si and its ionization potentials and electron affinities

The geometric structures and isomeric stabilities of various stationary points in C(2)H(2)Si neutral and its cation and anion are investigated at the coupled-cluster singles, doubles (triples) [CCSD(T)] level of theory. For the geometrical survey, the basis sets used are of the Dunning's correlation consistent basis sets of triple-zeta quality (cc-pVTZ) for the neutral and cation. For the anions, the cc-pVTZ basis sets with diffuse functions (aug-cc-pVTZ) are used. The final energies are calculated by the use of the CCSD(T) level of theory with the aug-cc-pVTZ basis set at their optimized geometries. To lower lying neutrals and cations, the Dunning's correlation consistent basis sets of quadruple-zeta quality (cc-pVQZ) are also applied. Both the global minima of the C(2)H(2)Si neutral and cation, N-1 (C(2v):(1)A(1)) and C-1 (C(2v):(2)B(2)), respectively, are silacyclopropenylidene conformers, having a CCSi ring with a C[Double Bond]C double bond. No competitive stable isomers exist in the present C(2)H(2)Si neutral. In the cation, however, the second lowest lying isomer C-2 lies 10.8 kJ/mol above the most stable C-1. The vertical and adiabatic ionization potentials from the lowest lying neutral N-1 are 9.83 and 8.97 eV, respectively, at the CCSD(T)/cc-pVQZ level of theory. The electron addition to the N-1 does not result in the anion with positive (real) electron affinities. On the other hand, the electron addition to the N-2 isomer produces the global minimum anion A-1 (C(2v):(2)B(1)) with the positive electron affinities of 1.13 eV. The second lowest lying anion isomer A-2 with silylenylacetylene conformer, produced from an electron addition to the N-3 neutral, very well competes with the A-1 after the zero-point vibrational energy corrections. The energy difference between the two lowest lying isomers of the neutral and its anion, N-1 and A-1, is only 0.39 eV.