High-resolution infrared rovibrational studies of the A1 species fundamentals of isotopic ketenes

Abstract The four A 1 -species fundamentals of ketene have been analyzed at a resolution of 0.05 cm −1 . Assignments are made for J ≤ 36 and K a ≤ 7, and asymmetry splittings observed for K a ≤ 2. Although individual subband analyses can be made, yielding upper state B , C , and B constants, all four bands exhibit irregular subband origins such that in no case can an accurate vibrational origin be determined. The rather close-lying perturbing levels can almost certainly be identified but no strictly quantitative interpretation of the perturbations can be made. Studies of the spectra of H 2 13 C 12 CO and H 2 12 C 13 CO confirm the origin of these perturbations. They are particularly acute in the cases of ν 3 (∼ 1387 cm −1 ), in Fermi resonance with ν 8 + ν 9 , and of ν 4 (∼ 1116 cm −1 ), in Fermi resonance with ν 5 + ν 6 , and also 2 ν 5 and 2 ν 6 . Indeed, in the latter case, it is debatable whether the observed band should be called ν 4 at all. On the other hand, analyses of the 2 ν 8 overtones of the CH 2 rocking fundamentals in the isotopic ketenes show little evidence of the effects of vibrational perturbations. The four fundamentals of dideuteroketene have also been studied; only ν 1 would appear to be essentially unperturbed.