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 Title: MILLIMETER−WAVE−MILLIMETER−WAVE DOUBLE RESONANCE SPECTROSCOPY Author(s): Schlemmer, Stephan Contributor(s): Thorwirth, Sven ; Lewen, Frank ; Müller, Holger S. P.; Bonah, Luis ; Zingsheim, Oliver Subject(s): Instrument/Technique Demonstration Abstract: Complex organic molecules 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 region are essential for identifying molecules in space. Double resonance techniques can help to solve these challenges. We present first millimeter-wave$-$millimeter-wave double resonance (DR) spectra to unambiguously assign new pure rotational lines of propanal (C$_2$H$_5$CHO). As already shown in chirped pulse Fourier transform microwave (CP-FTMW) experiments\footnote{D. Schmitz et al., \textit{J. Phys. Chem. Lett.} \textbf{6} (2015) 1493}, 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 technique (pulse modulation of pump and frequency modulation of 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 and possible future applications, such as automatization and incarnation of baseline-free DR spectroscopy in chirped pulse experiments. Issue Date: 23-Jun-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/107470 Date Available in IDEALS: 2020-06-26
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