High-Throughput Microwave Spectroscopy for Chemical Kinetics and Trace Detection

Recent advances in high-speed digital electronics have made it possible to construct direct digital broadband microwave spectrometers in the 2-18 GHz frequency range. Microwave chirped pulse excitation is used to coherently excite the molecular rotational spectrum over a bandwidth of up to 12 GHz. Phase-reproducible excitation pulses are generated using a 24 Gs/s arbitrary waveform generator and permit time-domain averaging of the broadband coherent molecular emission. The molecular emission is directly digitized using an 8-bit, 50 Gs/s digitizer and the spectrum obtained from subsequent fast Fourier transformation. The sensitivity of the spectrometer makes it possible to detect the broadband rotational spectrum using ~100 pmol sample injection in a measurement time less than 1 ms. The spectrometer has been used to measure quantum-state-resolved rotational spectra of highly vibrationally excited molecules prepared by pulsed-laser excitation. In cases where the molecule is excited above the barrier to isomerization, these dynamic rotational spectra provide measurement of the unimolecular isomerization rate. The spectrometer also has applications for chemical analysis including the identification of high-energy isomers, radicals, and ions produced in discharge sources. Experiments designed to produce potential interstellar molecules will be presented.

For more information contact Prof. Ken Brown (404-385-3124).