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 Title: OBSERVATION OF VIBRATIONALLY EXCITED STATES OF SiC2 BY STIMULATED EMISSION PUMPING Author(s): Reilly, Neil J. Contributor(s): McCarthy, Michael C; Flores, Jonathan ; Lee, Kelvin ; Ross, Sederra D. Subject(s): Astronomy Abstract: Recent observations of the evolved carbon star IRC+10216 with unprecedented high angular resolution have revealed a plethora of unassigned (U) rovibrational lines associated with the dust formation zone. Because SiC$_2$ is a known, abundant molecular constituent of this region, it is reasonable to posit that some fraction of the observed U lines arise from vibrationally excited levels of SiC$_2$ that are populated at elevated temperatures. At present, the radio band laboratory data that would permit testing of this hypothesis are largely absent: \textit{ab initio} prediction of relevant spectroscopic parameters for SiC$_2$ has proved particularly challenging, and its excited vibrational levels are insufficiently populated in supersonic jet sources. However, the electronic transition responsible for the well-known blue-green Merrill-Sanford bands of SiC$_2$ admits Franck-Condon access to vibrational levels at least 4000\,K above ground, inviting the application of stimulated emission pumping (SEP) for the observation of vibrationally excited states. SiC$_2$ has been efficiently generated in a jet-cooled discharge of silane and acetylene, optically pumped via the M-S bands, and fluorescence depletion SEP spectra observed for dump transitions terminating in a variety of excited vibrational levels of the ground electronic state. For known transitions within 1$\nu_3$ and 2$\nu_3$ (the pinwheel mode), our measurements are in generally excellent agreement (a factor of at least 5 smaller than the dump laser linewidth) with previous observations, giving us good faith in our experimental procedure; rotational analyses of previously unobserved transitions of all three vibrational modes are on-going at the time of writing, and will be discussed. Issue Date: 24-Jun-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/107616 Date Available in IDEALS: 2020-06-26
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