New analysis of the ν6 and 2ν3 bands of methyl iodide (CH3I)

Abstract

A new rovibrational study of the ν6 band of methyl iodide was conducted to obtain a rather complete line list. A new analysis of line positions was accomplished. The spectrum of this band has been first recorded using the Bruker IFS125HR Fourier transform spectrometer (FTS) at the AILES beamline of the SOLEIL Synchrotron facility and later with the Bruker IFS125HR FTS located at the LISA facility in Créteil. Altogether, about 10,000 lines were assigned for the ν6 and 2ν3 bands up to high quantum numbers (J⩽85 and K⩽20). Because of the large value of the 127I nuclear quadrupole hyperfine constant, a significant portion of these assignments concerns clusters of hyperfine subcomponents, which are easily observable at 11μm. These infrared data were combined in a least squares fit together with the existing microwave data on rotational transitions within the v6=1 and v3=2 vibrational states to get the upper state rotational constants and interacting parameters for the v6=1 and v3=2 states. Due to the high values of quantum numbers achieved during this infrared analysis, the final energy level calculation accounts for aCx(Δℓ=±1;ΔK=±1) and an α(Δℓ=∓1;ΔK=±2) types of Coriolis interactions coupling the v6=1 energy levels with those from the v3=2 and v2=1 states, respectively. On the other hand, it proved unnecessary to update the existing hyperfine parameters for the v6=1 and v3=2 states.