Fourier transform infrared spectroscopy of the 2ν3 overtone band of different ICN isotopomers: an improved evaluation of the anharmonic force field of cyanogen iodide

The weak 2ν₃ overtone band of the three isotopomers of cyanogen iodide, I¹²C¹⁴N, I¹³C¹⁴N, and I¹²C¹⁵N, has been recorded in the range from 4200 to 4400 cm⁻¹ with a resolution of 0.02 cm⁻¹ using a Fourier transform infrared spectrometer. The following band origins have been determined from the analysis of the spectra: ν₀ (I¹²C¹⁴N)=4332.8368 cm⁻¹, ν₀ (I¹³C¹⁴N)=4235.7355 cm⁻¹, and ν₀ (I¹²C¹⁵N)=4274.2851 cm⁻¹. This allowed us to achieve complete knowledge of the energies for all levels of ICN corresponding to double vibrational excitation. An improved evaluation of the quartic force field of cyanogen iodide has been performed using the new data obtained together with those already known from previous works.