Detailed analysis of ν5 of CH3I: Fermi and Coriolis resonances with ν3+ν6 and ν2

The high‐resolution infrared spectrum of ν₅ of CH₃I reported in the previous paper [J. Chem. Phys. 55, 1787 (1971)] has been reanalyzed. By extending the assignment of the observed lines and by taking account of the xy‐type Coriolis interaction with ν₂ in addition to the Fermi and xy‐type Coriolis resonances with ${\nu }_3{\mathrm{+\nu }}_6$ , the rotational constants have been determined to be B ₅(unp) = 0.25015₉ cm⁻¹ and B _3,6(unp) = 0.24763₁ cm⁻¹ which are now consistent with the microwave results. The l‐type doubling constant has been obtained to be ${\mathrm{q\hspace{0.17em}}}_5(\mathrm{unp}{\text{)=−2.2× 10}}^{\text{−5}}\hspace{0.17em}{\mathrm{cm}}^{\text{−1}}$ . The Fermi resonance term has been found to depend on the quantum number J.