The far infrared rotational spectrum of HOBr: line positions and intensities

Abstract

The far infrared absorption spectrum of HOBr has been measured at high resolution between 100 and 400 cm −1 using high-resolution Fourier transform spectroscopy. It was possible to identify not only 1403 pure rotation lines within the vibrational ground state involving levels with rather high K a quantum numbers (up to K a=9) but also 457 pure rotation lines within the first excited vibrational state 3 1 up to K a=7. The ground state lines, combined with 32 microwave transitions available in the literature, were used for a new determination of the rotational constants up to higher orders for both isotopomers HO 79Br and HO 81Br, by least squares fitting of the observed line positions using a Watson-type Hamiltonian for the calculation of rotational energy levels. In the same way the 3 1 rotational lines were fitted together with the few existing microwave transitions and the energy levels derived from the study of the ν 3 band ( J. Orphal, Q. Kou, F. Kwabia Tchana, O. Pirali, and J.-M. Flaud, J. Mol. Spectrosc. 221 (2003), 239–243) leading to an improved set of Hamiltonian constants. Finally relative line intensities were measured and used for the determination of rotational corrections to the b-component of the permanent dipole moment.