title: Improved sensitivity of tunable far-infrared spectroscopy: application to the detection of HBr in the ? = 1 state.
abstract: We report the first detection of the pure rotational spectra of H79 Br and H81 Br in the first excited vibrational state at room temperature. We recorded the spectra with a tunable far-infrared spectrometer equipped with an optimized Ge:Ga photodetector and an improved multiple-pass gas cell to enhance the overall sensitivity. In particular, a minimum detectable absorption of better than 10-7 cm-1 was achieved. We measured a total of 60 frequencies for the two isotopomers with an accuracy of a few parts in 108 . The hyperfine structure was observed at the lower J values. The derived spectroscopic parameters, which include nuclear and quadrupole hyperfine constants, reproduce the assigned transitions within their experimental errors.
authors.forename: P
authors.initials: P
authors.lastname: De Natale
authors.forename: L
authors.initials: L
authors.lastname: Lorini
authors.forename: M
authors.initials: M
authors.lastname: Inguscio
authors.forename: G
authors.initials: G
authors.lastname: Di Lonardo
authors.forename: L
authors.initials: L
authors.lastname: Fusina
authors.forename: P A
authors.initials: PA
authors.lastname: Ade
authors.forename: A G
authors.initials: AG
authors.lastname: Murray