15min:

J.-M. FLAUD, Laboratoire de Photophysique Moléculaire, C.N.R.S., Bât. 350, Université Paris-Sud, 91405 Orsay Cedex, France; W. J. LAFFERTY, Optical Tech. Division, NIST, Gaithersburg, MD 20899-8440, USA; M. HERMAN, Lab. de Chimie Physique Moléculaire, Université Libre de Bruxelles, 50 Av. Roosevelt, 1050-Brussels, Belgium.

The rotational structure of the ₁₉ (CH₂-wagging, A-type band), ₁₈ (CH₃-s-deformation, A-type band), ₂₄ (CH₃-d-deformation, C-type band), and ₄ (CH₃-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 19¹ and 18¹ states. However, to properly calculate the rotational levels of the 4¹ and 24¹ 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 5¹ and 17¹ vibrational states. It is then possible to calculate the upper-state levels to within an average uncertainty of 2 to 5 × 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 ₀( ₁₉)=1338.965~cm^-1, ₀( ₁₈)=1376.850~cm^-1, ₀( ₂₄)=1471.874~cm^-1 and ₀( 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.