The Effect of Nuclear Quadrupole Hyperfine Interaction on the Infrared Absorption Band ν6 of 12CH3I

Abstract A high-resolution absorption spectrum of the perpendicular fundamental ν 6 of 12 CH 3 I was recorded. The band was analyzed essentially as an unperturbed perpendicular band, although a small Coriolis interaction with 2ν 3 was taken into account. A least-squares fit with 19 molecular parameters was performed. The splittings and shifts in line positions caused by the nuclear quadrupole hyperfine effect were investigated, and the influence of this effect on the results of the least-squares fit was studied. The correction of the hyperfine effect increases the amount of acceptable lines by more than 10% in the least-squares fit. The influence of these additional observations on the molecular constants is generally within the statistical error limits, but for some higher order parameters the changes are more considerable.