L-RESONANCE EFFECTS IN THE NU(5),2-NU(5)[-NU(5), AND NU(4)+NU(5)[-NU(4) BANDS OF C2H2 AND (CCH2)-C-13-C-12 NEAR 13.7-MU-M

An extension to the previous LSCD (lower state combination difference) determination of molecular parameters involving acetylene's nu5 fundamental and the strongest one quantum hotbands, 2nu5 <-- nu5 and nu4 + nu5 <-- nu4 [J. Molec. Spectrosc. 146, 389 (1991)] has been made. A novel iterative numerical diagonalization procedure was employed to fit the vibrational states involved in the seven one quantum hotbands. This method utilizes the Hellmann-Feynman theorem to calculate first derivatives and singular value decomposition (SVD) in its least-square procedure and permits the simultaneous evaluation of the effective dipole moment responsibie for the l-type resonance effect upon IR intensities. A set of molecular parameters describing the rotation-vibration levels of the ground state, nu5, nu4, 2nu5 and nu4 + nu5 for the major isotope and for (CCH2)-C-13-C-12 are reported based upon FT-spectrometric data taken at the McMath Solar Telescope Observatory. The improved spectroscopic parameters retrieved from this investigation will serve as a database for modelling abundances of acetylene in various astrophysical sources.