Knowledge Bank

The pure rotation spectrum of natural HOCl has been recorded between 40 and $300cm-1$ by Fourier transform spectrometry. In the lower spectral region where appear rather strong low $Ka$ subbands a particle density of about $1.2\times 1013/cm3$ was used while in the upper region a mean particle density of $2.1\times 1013/cm3$ was achevied in order to measure also weak high $Ka$ subbands. The observed line positions, together with other data available in the literature (microwave, far-infrared, combination differences), were least squares fitted to within their experimental accuracy both for $HO35Cl$ and $HO37Cl$ using a Watson-type Hamiltonian. Also line intensities were measured for both isotopic species and least square fitted allowing the determination of some weak rotational correcting terms appearing in the dipole moment expansion. As a quality test of the intensity measurements it is worth noticing that the ratio of the total band intensities of $HO37Cl$ and $HO35Cl$ was found to be $0.3188$ in excellent agreement with the isotopic ratio (0.3198).