Theoretical study of structures, energetics and vibrational properties of BC2H5 species Original Research Article

Hybrid density functional theory (B3LYP) and quadratic configuration interaction including single and double excitations (QCISD) methods with the Dunning correlation consistent polarized valence double zeta (cc-pVDZ) basis set have been used to examine the structures, vibrational spectra and stabilities of the singlet spin multiplicity molecular species with BC2H5 stoichiometry. Six isomers have been located. Total energies, refined at the CCSD(T)/cc-pVTZ//B3LYP/cc-pVDZ level, predict vinylborane molecule (H2BCHCH2, Cs) to be the absolute minimum followed by the H2CBCH3 molecule (Cs), 2.3 kcal/mol less stable. Borirane (HB(CH2)2, C2v with BC2 ring) and HBCHCH3 (Cs) molecules are calculated, respectively, to be 13.5 and 18.5 kcal/mol higher than vinylborane. The BH3:C2H2 donor–acceptor complex is found about 42 kcal/mol higher than vinylborane. Ethylborine molecule BCH2CH3, the highest energy isomer, is predicted 45 kcal/mol above the absolute minimum. The calculated vibrational spectra for H2BCHCH2 and H2CBCH3 agree with the recent matrix isolation experiments and confirm their argon matrix IR characterization.