Detection and Measurements of Air Pollutants and Constituents by Millimeter-Wave Microwave Spectroscopy

Abstract

The properties of millimeter-wave spectrometers as highly specific and sensitive experimental research tools for monitoring gaseous pollutants of interest in pollution research are presented. A spectrometer system operating at frequencies in the vicinity of 70 GHz~ld employing a semi-confocal Fabry-Perot resonator as the sample cell is described. The resonator is voltage tuned by means of a piezoelectric transducer which enables it to track the microwave source frequency. The operation and performance of the spectrometer are discussed and illustrated by measurements of diluted samples of sulfur dioxide. The noise from the microwave source, the absorption cell and the receiver, which ultimately limits the achievable sensitivity are discussed along with considerations for future sensitivity improvements.

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70–102 GHz region

“…The transition frequency was previously reported as 76 229.027 (20) MHz. 44 In the current work, we correct this frequency to 76 263.89 (10). The FWHM is 1.1 MHz and is attributable to the radiative lifetime of the e 3 − state.…”

“…The advantage of these spectral regions derives primarily from the extremely high resolution and accompanying high frequency accuracy that they provide. The millimeter-wave region has proven particularly important for measurements on small molecules with large rotational constants, [1][2][3] studies of pure-electronic Rydberg-Rydberg transitions, [4][5][6][7][8][9] sensitive detection of molecules at room temperature, [10][11][12] and detection of astronomical molecules. 13 Much recent progress has been made in the development of methodology for gas-phase millimeter-wave spectroscopy.…”