Abstract:
Interesting rovibrational characteristics of two D_(3h) oblate symmetric top molecules were studied. Hamiltonian models for the fine rovibrational level structure of [1.1.1]propellane (propellane) were obtained for many low-lying modes. Ground state parameters (GSP) that are not exclusively K^(2n) dependent were obtained. Initially, the GSP were used in conjunction with density functional (DFT) values of the exclusively K^(2n) dependent parameters C_0, and D_e. Coriolis h_(1,1) (deltaK = +/-1, deltal = +/-1) interactive fundamentals nu_(15) and nu_(12) were analyzed; complementary use of transition energies and line intensities allowed an experimental value of the Coriolis parameter to be assessed. In another phase of the project, a global fit of the nu_(10), nu_(11), and nu_(14) fundamental bands and the nu_(11)-nu_(18) and nu_(10)-nu_(18) bands was performed. The h_(1,1) interaction between the close proximity rovibrational states of nu_(11) and nu_(14) results in energy shifts and large distortions of line intensities in the nu_(11) band, and these characteristics were reproduced. Splitting of the otherwise degenerate A_1 and A_2 states that are the highest in frequency for a given J manifold was observed for the h_(1,1) coupled nu_(11) /nu_(14) triad composed of the |k| = 3 levels of nu_(14) , the kl = + 4 levels of nu_(11), and kl = -2 levels of nu_(11). Significant splitting of the kl=-2 levels in combination with h_(1,1) are important in the noted lifting of degeneracies. Another interaction, this one between nu_(14) and what is presumably the IR inactive nu_(16)/nu_3 singly excited dyad, results in a significant bifurcation of the K levels of nu_(14) for a given observable J manifold. Another interaction, h_(5,-1), between nu(14) and nu_(11), made it possible to find C_0 and D_K 0, parameters not available from analysis of transitions from the ground vibrational state to singly excited fundamentals in the absence of higher order interactions. In studies of another D_(3h) oblate top, BF_3, effects of anharmonic interactions on the band origin of the symmetric stretching mode were examined using coherent anti-Stokes Raman spectra of ^(10)BF_3 and ^(11)BF_3. Upon isotopic substitution, the magnitude and direction of the anharmonic shifts of each fundamental were observed to be consistent with DFT results.
