The first high-resolution analysis of the low-lying ν9 band of propane

The ν9 fundamental band (C-C-C deformation) of propane (C3H8) at 369 cm−1 has been studied at high-resolution (0.0011 cm−1) with spectra recorded using the synchrotron radiation from the French light source facility at SOLEIL coupled to a Bruker IFS 125HR Fourier transform spectrometer. A 2.526 m base multipass cell with optical paths from 10.296 to 151.78 m was used. In addition, a spectrum was also recorded using a conventional globar source. Comparison of these experimental spectra shows clearly the gain obtained on the signal-to-noise ratios with the synchrotron radiation. The spectra have been thoroughly analyzed and transitions up to J=65 and Ka=33 have been assigned. The upper-state rotational levels were fitted using an A-type Watson Hamiltonian written in the Ir representation. An accurate band center ν0 (ν9)=369.228080(25) cm−1 as well as accurate rotational and centrifugal distortion constants have been obtained and used to simulate a synthetic spectrum. These parameters should be useful to simulate hot bands of propane involving the 91 vibrational level as their lower state.