Two aluminum mirrors with radii of 203.2 mm and radii of curvature also of 203.2 mm have been used to construct a tunable Fabry-Perót type resonator with Q values of ∼200 at frequencies as low as 500 MHz. The resonator has been incorporated into a pulsed nozzle, Fourier transform, Balle-Flygare spectrometer typically used for recording pure rotational spectra in the microwave region. The resonator design allows the instrument to access the radio frequency region (≤3 GHz) of the electromagnetic spectrum. The spectrometer is of use in (i) recording low J transitions of large asymmetric molecules where the spectra are often greatly simplified compared to higher frequency regions; (ii) measuring hyperfine constants for heavy molecules with higher accuracy than may be obtained at higher frequencies where hyperfine structure may not be resolvable; and (iii) provides further synchronicity between laboratory based measurements and radio astronomy in the 30 cm region. The resonators use is illustrated by recording the rotational spectra of bromobenzene and iodobenzene. The lowest ΔJ = +1 transition for iodobenzene has been observed at 1130.5292(10) MHz.
Bibliographical noteFunding Information:
We are happy to acknowledge numerous conversations with Prof. Jens-Uwe Grabow at the University of Hannover. We thank Prof. Sean Peebles at Eastern Illinois University for providing complete line listings for bromobenzene. The hemispherical resonators were polished and mounted in the vacuum chamber by Mr. Kurt Weihe and Mr. Bobby Turner of the Physics Department machine shop at the University of North Texas. Bromobenzene and iodobenzene were kindly donated by Profs. Michael Richmond and Trent Selby, respectively, both at the Chemistry Department in the University of North Texas. This research has been financially supported by the University of North Texas through start up funding and a Junior Faculty Summer Research Fellowship and by the Petroleum Research Fund (type G), administered by the American Chemical Society.
Copyright 2008 Elsevier B.V., All rights reserved.
- Low frequencies
- Rotational spectroscopy