Line positions in the v6=1 band of methyl iodide: Validation of the C3v TDS package based on the tensorial formalism

- A line position assignment of the v6 of methyl iodide is done.
- A validation of the C3v TDS package of the XTDS suite of programs based on the tensorial formalism is proved.
- A further improvement of the C3v TDS package is proposed in order to include hyperfine structure effects.

A tensorial formalism adapted to the case of symmetric-top molecules has been recently developed in Dijon (El Hilali et al., J Quant Spectrosc Radiat Transf 2010;111, 1305-1315) [18]. It is based on the O(3)⊃C∞v ⊃C3v group chain and allows a systematic expansion of the Hamiltonian and dipole moment operators, including all possible interactions for a given rovibrational polyad system. This suite of programs is used to analyze and simulate the mid-infrared spectrum of methyl iodide in order to test its performance. The v6 fundamental band has been recorded using the FTIR Bruker HR125 at the AILES beamline of the SOLEIL Synchrotron facility with the Globar internal source. 3882 lines up to J=61 were assigned and fitted with only 16 tensorial parameters.