FIRST VIB-ROTATIONAL ANALYSIS OF PROPANE AROUND $7 \mu m$ USING JET SPECTRA

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2001

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Ohio State University

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The rotational structure of the $\nu_{19} (CH_{2}$-wagging, A-type band), $\nu_{18} (CH_{3}$-s-deformation, A-type band), $\nu_{24} (CH_{3}$-d-deformation, C-type band), and $\nu_{4} (CH_{3}$-d-deformation, B-type band) vibrational fundamentals of propane, were recorded using a molecular beam coupled to a Fourier-transform spectrometer working at $0.005 cm^{-1}$ resolution. The analysis was performed using Watson Hamiltonians for the $19^{1}$ and $18^{1}$ states. However, to properly calculate the rotational levels of the $4^{1}$ and $24^{1}$ vibrational levels, it is necessary to include in the Hamiltonian matrix not only the strong A-type Coriolis interaction which couples them but also the various interactions (Coriolis or Fermi-type) which link them to the levels of the dark $5^{1}$ and $17^{1}$ vibrational states. It is then possible to calculate the upper-state levels to within an average uncertainty of 2 to $5 \times 10^{-3} cm^{-1}$ depending on the state. These results are satisfactory given the fact that (i) possible perturbations with nearby combination states were not considered and (ii) several torsional splittings were not accounted for. The band centers derived from the fits are $\tilde{\nu}_{0}(\nu_{19}) = 1338.965 cm^{-1}$, $\tilde{\nu}_{0}(\nu_{18}) = 1376.850 cm^{-1}$, $\tilde{\nu}_{0}(\nu_{24}) = 1471.874 cm^{-1}$ and $\tilde{\nu}_{0}(\nu_{4}) = 1476.710 cm^{-1}$. The standard uncertainties of these values are estimated to be about $0.002 cm^{-1}$, which includes the calibration errors as well as the statistical uncertainty of the fittings.

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Author Institution: C.N.R.S., B\^at. 350, Universit\'e Paris-Sud; Laboratoire de Photophysique Mol\'eculaire, Optical Tech. Division; Laboratoire de Photophysique Mol\'eculaire, Universit\'e Libre de Bruxelles

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