We have observed and analyzed the first overtone triad of the v1 and v7 CH stretching modes of ketene in the range of 60006300 cm-1. The Ka = 0 components of all three bands could be assigned based on missing Q-branches and combination differences, allowing an unambiguous determination of the rotationless band origins for the 2v1, v1 + v7, and 2v7 bands. In addition, the Ka = 1, 2, and 3 subbranches as well as some higher Ka stacks were assigned for all three bands. The 2v7 band suffers from the most serious Coriolis perturbations, while at least some subbranches of the other bands could be fitted together. The anharmonic coupling structure perturbing the CH stretching overtones is discussed in terms of a quartic anharmonic force field derived from eight pair GVB/RCI calculations. Finally, an assignment of the Ka - 1 and Ka = 3 subbands of the 2v2 CO stretching overtone is also presented, together with an estimate of the rotationless band origin. A coincidence of several subbands prevented the unambiguous assignment of the Ka = 0 stack in this case.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry