A multioctave coaxially oriented beam-resonator arrangement Fourier-transform microwave spectrometer

Abstract

The design, performance, and operation of a broadband (3–26.5 GHz) high resolution microwave spectrometer is described. In comparison to previously developed molecular beam Fabry–Perot resonator spectrometers the design presented here implements some significant improvements: a coaxially oriented beam resonator arrangement (COBRA) formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas, and a multioctave Fourier-transform microwave (FTMW) instrument providing the pulsed excitation source with microwave pulse phase-inversion scheme and the low-noise receiving system employing image-rejection downconversion with superheterodyne as well as quadrature detection. The entire apparatus, fully automated for scanning operation, covers a frequency range of more than three octaves. The novel design of the FTMW instrument does not require any changes of the spectrometer hardware in order to reach all regions of its spectral range. While operated in high resolution mode the COBRA-FTMW spectrometer is achieving a linewidth (half-width at half-height, HWHH) relative to the molecular emission frequency of better than 10−7 HWHH. The sensitivity and resolution of the spectrometer is demonstrated by several examples.

Rapid probe of the nicotine spectra by high-resolution rotational spectroscopy

“…2 for 7 1,6 -6 1,5 rotational transition) but the spectral widths of the resonances in the COBRA-FTMW spectrum are noticeably smaller due to the coaxial arrangement of the supersonic jet with respect to the resonator. 17 The hyperfine structure was then resolved for all observed rotational transitions. Up to 182 and 129 hyperfine components were measured for I and II rotamers, respectively.…”

“…15 The present study on nicotine follows our interest to examine relevant biomolecules by the high resolution of microwave spectroscopic techniques. The combination of supersonic-jets with Fourier transform microwave (FTMW) spectroscopy [16][17][18] has proved to be a powerful tool in the investigation of the conformational behavior of gas phase biomolecular systems. In such studies, vaporization of biomolecules is achieved through the laser ablation molecular beam (LA-MB-FTMW) technique 19,20 or heating methods.…”

Conformational steering in dicarboxy acids: the native structure of succinic acid

“…The rotational spectrum of succinic acid was recorded using three spectrometers: the spectra in the cm-wave region (7-26 GHz) were obtained using two high-resolution pulsed supersonic jetexpansion Fourier transform microwave (FT-MW) spectrometers of Balle-Flygare-type 39 in Hannover (2-26 GHz) 40 and Bilbao (4-18 GHz), 41 both using the COBRA technique. 42 In the 48-70 GHz mm-wave region the spectra were recorded using a free-jet, Stark-modulated absorption spectrometer at Monash University, that has been modified with solid state sweep oscillator sources.…”

“…42 In the 48-70 GHz mm-wave region the spectra were recorded using a free-jet, Stark-modulated absorption spectrometer at Monash University, that has been modified with solid state sweep oscillator sources. 43 The three instruments have been described extensively; [40][41][42][43] therefore, only brief experimental details are given here. The solid sample was inserted inside a reservoir located at the nozzle exit and heated at 110-180 1C in the Hannover and Monash spectrometers.…”

Specific Millimeter-Wave Features of Fabry-Perot Resonator for Spectroscopic Measurements

“…As in our practice case, the source input power of 10 dBm was chosen. The principle of the electric field distribution in transverse plane is demonstrated for instance in (Grabow, 1996) and (Kogelnik, 1966). A longitudinal distribution of the electric field intensity of distinguishable TEM modes inside the resonator is shown in Fig.…”