The Far Infrared Spectrum of HOCl: Line Positions and Intensities.

The far infrared spectrum of HOCl has been recorded at high resolution between 20 and 360 cm-1 by means of Fourier transform spectroscopy, and it was possible to observe pure rotation lines involving rotational levels with high Ka quantum numbers (up to Ka = 9). These lines combined with microwave and tunable far infrared data available in the literature were least squares fitted using a Watson-type Hamiltonian. The fitting leads to precise sets of rotational and centrifugal distortion constants for the ground states of both isotopomers HO35Cl and HO37Cl. Also relative line intensities were measured and their fitting allowed the determination of rotational corrections to the b-component of the permanent transition moment. Finally, to get Hamiltonian constants consistent with the newly determined ground state constants for the (100), (010), (001) vibrational states, available data concerning the nu1, nu2, and nu3 bands were refitted. Three interesting points are to be stressed. For the (001) state, we were able to complete the existing data with rotation lines observed in our spectra up to rather high Ka values (Ka = 7). For HO35Cl, we were able to show that some (010) and (100) levels are perturbed by levels of the (002) and (030) states, respectively, through Coriolis-type interactions. This allows the determination of the band centers of these two dark states. Copyright 1998 Academic Press.