Deperturbation of the low-frequency infrared modes of ketene (CH2CO)

Abstract In this paper we report an asymmetric rotor analysis of the room temperature Fourier-transform infrared gas phase spectrum of ketene (CH 2 CO) at near Doppler limited resolution. The four fundamental modes below 1000 cm −1 ( ν 5 , ν 6 , ν 8 and ν 9 ) are influenced by global z -axis Coriolis perturbations. Using a general non-linear least-squares fitting program developed at the ETH Zurich to determine perturbation parameters and deperturbed molecular constants we have re-analysed the FTIR spectrum to free the effective rotational constants from Coriolis contributions. First-order z -axis Coriolis zeta constants connecting the above four fundamentals were determined. Strong local perturbations for the K ′ a =0 and 1 states are observed for the ν 8 vibrational state.