The rotational structure of the n19 (CH2- wagging, A-type band), n18 (CH3- s-deformation, A-type band),n24 (CH3- d-deformation, C-type band), and n4 (CH3- d-deformation, B-type band) 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's 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 x 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 (n19) = 1338.965 cm-1, (n18) = 1376.851 cm-1, (n24) = 1471.874 cm-1 and (n4) = 1476.705 cm-1. The standard uncertainty of these values is 0.002 cm-1, which includes calibration errors as well as the statistical uncertainty of the fittings.
Citation: Journal of Chemical Physics
Issue: No. 21
Pub Type: Journals
high resolution, infrared spectrum, molecular beam, propane, spectroscopic constants