Magnetic hyperfine structure and centrifugal distortion in quadrupole spectra of 12CH3I and 13CH3I

Quadrupole spectra of ¹²CH₃¹²⁷I and ¹³CH₃¹²⁷I in the ground vibrational state have been recorded at high resolution (1–2 KHz) using a radiofrequency-microwave double-resonance spectrometer. The magnetic structure of the quadrupole transitions has been resolved and analyzed. Spin-spin and spin-rotation interaction parameters have been determined, together with accurate values of the quadrupole coupling constants and their centrifugal corrections. Comparison with theory is made by using isotopic relations for the two species of iodomethane.