Knowledge Bank

The spectrum of ketene has been recorded1 in the C-H symmetric stretch region at Doppler resolution with an infrared laser difference-frequency spectrometer. The spectrum is plagued with perturbations, of both global (all J levels within a $K5$ stack) and local type (few J levels affected, sign reversal in obs-calc at a given J). Local perturbations have been interpreted by means of a simple $2x2$ matrix model for each $J,Ka,Ks$ level, making use of three possible sources of data: obs-calc shift, assignment of transitions (P and R) to the perlurbing level of the dark band, and predicted intensity pattern. Most of the crossings found in this spectrum are very localized, which allows to obtain very limited information on the perturbing band, although an approximate value of the perturbation parameer is always found. The first conclusions seem to imply that most of the perturbations arise from different vibrational states. This is favored by the special characteristics of symmetry and energy of the vibrational levels of this molecule, which pernit several Coriolis and Fermi resonances to take place in this region.