CP-FTMW Broadband spectroscopy from 2 to 60 GHz
      Because of the high spectral purity of microwave light sources and high dynamic range, Chirped Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy provides unparalleled ability to unambiguously determine molecular structure. Since the rotational transition frequencies of a given species are determined purely by the moments of inertia of the molecule, mass shifts due to isotopic substitution generally cause relatively large shifts in transition frequency with respect to the spectral resolution. The acquisition and assignment of isotopically substituted spectra of a target species allow us to determine, with application of Kraitchman’s equations or least linear squares fitting (see OSU ISMS talk: 2012 RH03), accurate experimental molecular structures with precision at the level of a few picometers. Thankfully, the high dynamic range of CP-FTMW generally allows for detection of the most common heavy atom isotopologues in natural abundance, as well. For representative results, see our recent talks in the Publications section of this website.

      Although traditional cavity-based microwave methods can provide better resolution on specific spectral features of a target molecule, CP-FTMW provides unparalleled speed and resolution for highly complex broadband spectra arising from mixtures of reaction products (2011 WF01), isomers (2009 MH01; TA05), or weakly bound molecular clusters (2012 MH13; MH14; RH02-03, amongst others). The combination of the predictive power of computational chemistry for structure and automated data analysis techniques being developed here in the Pate lab have led to a push towards library-free detection, where molecular/structural assignment can be made without any spectroscopic foreknowledge of the target species. For further information on Autofit, a detailed description and download link are available in the Useful Stuff section of this website.

      Since the speed of CP-FTMW is constrained by the speed of the detection hardware, new developments in digitization are integral in improving the effectiveness of the technique. For instance, our recent move from Tektronix' 50 Gs/s, 20 GHz bandwidth DPO7200-series oscilloscope to their new 100 Gs/s, 33 GHz bandwidth DPO7300-series oscilloscope has improved the speeed of signal averaging by nearly an order of magnitude. Additionally, the move to a larger hardware bandwidth has allowed for new direct detect techniques in higher frequency bands such as 25-40 GHz, significantly simplifying the technique by removing the need for mixing down the molecular signal.

2011 Nova all rights reserved. Luiszuno.com