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Title:Millimeter-millimeter-wave Double-modulation Double-resonance Spectroscopy
Author(s):Zingsheim, Oliver
Contributor(s):Schlemmer, Stephan; Thorwirth, Sven; Lewen, Frank; Müller, Holger S.P.; Bonah, Luis
Subject(s):Instrument/Technique Demonstration
Abstract:Complex organic molecules (COMs) show regularly very rich spectra, sometimes at a line density close to the confusion limit. The plethora of lines often originates from the presence of different conformers and/or low-lying vibrational states. The analysis of spectra may considerably be further complicated by vibration-rotation or other interactions. However, accurate spectroscopic predictions in the millimeter-wave (MMW) region are essential for identifying molecules in space. Double-resonance techniques can help to solve these challenges. We present first MMW$-$MMW double-resonance (DR) spectra to unambiguously assign weak and perturbed rotational lines of propanal (C$_2$H$_5$CHO). As already shown in chirped pulse Fourier transform microwave (CP-FTMW)\footnote{D. Schmitz et al., \textit{J. Phys. Chem. Lett.} \textbf{6} (2015) 1493} and in MW$-$MMW DR experiments,\footnote{K.~M. Roenitz et al., \textit{J. Phys. Chem. A.} \textbf{122} (2018) 6321} the Autler-Townes splitting\footnote{S. H. Autler and C. H. Townes, \textit{Phys. Rev.} \textbf{100} (1955) 703} allows for distinguishing between regressive or progressive energy level schemes. The Autler-Townes splitting is clearly visible in our 2D spectra. Furthermore, implementation of a double-modulation double-resonance (DM-DR) technique, pulse modulation of the pump and frequency modulation of the probe source, allows for confusion- and baseline-free spectra containing only the line(s) of interest. We discuss details of the observed Autler-Townes splitting, benefits of simplified spectra, and possible future applications, such as automatization.
Issue Date:2021-06-22
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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