Lowest Overtone and Combination Levels of DCCI: The Fermi Resonancev3= 1/v5= 2

Abstract The infrared spectrum of deuterated monoiodoacetylene DCCI in the region of 220–550 cm −1 has been studied at a resolution of 0.0020 cm −1 . The hot bands ν 3 ← ν 1 5 and 2ν 0,2 5 ← ν 1 5 have been analyzed by considering especially the Fermi resonance v 3 = 1/ v 5 = 2. In the next layer of the hot bands (ν 3 + ν 5 ) 1 ← ν 3 , (ν 3 + ν 5 ) 1 ← 2ν 0,2 5 and 3ν 1,3 5 ← 2ν 2 5 the same Fermi resonance appears between v 3 = v 5 = 1 and v 5 = 3. In addition, various l resonances at the overtone levels have been considered. As a result, the vibrational and rotational constants for the level systems v 3 = 1/ v 5 = 2 and v 3 = v 5 = 1/ v 5 = 3 together with the resonance parameters have been obtained.