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 Title: Progress In Understanding The Infrared Spectra Of He- And Ne-c2d2 Author(s): McKellar, Bob Contributor(s): Moazzen-Ahmadi, Nasser Subject(s): Clusters/Complexes Abstract: Infrared spectra of He-C$_2$H$_2$ were recorded around 1990 in Roger Miller's lab, but detailed rotational assignment was apparently not possible even with the help of theoretical predictions. So there were no published experimental spectra of helium-acetylene van der Waals complexes until our recent work on He-C$_2$D$_2$ in the \nub{3} region ($\sim$2440 \wn).\footnote{M. Rezaei, N. Moazzen-Ahmadi, A.R.W. McKellar, B. Fernández, and D. Farrelly, Mol. Phys. \textbf{110}, 2743 (2012).} The problem is that this complex lies close to the free rotor limit, so that most of the intensity in the spectrum piles up in tangles of closely spaced lines located close to the monomer rotational transitions, $R(0)$, $P(1)$, etc. Our previous He-C$_2$D$_2$ assignments were limited to the $R(0)$ region, that is, the $j$ = 1 $\leftarrow$ 0 subband, where $j$ represents C$_2$D$_2$ rotation. Here, we extend the analysis to $j$ = 0 $\leftarrow$ 1 and 2 $\leftarrow$ 1 transitions with the help of new spectra obtained using a tunable OPO laser probe and a cooled supersonic jet nozzle. These subbands are weaker, not only because of the Boltzmann factor, but also the 2:1 nuclear spin statistics of $j"$ = even:odd C$_2$D$_2$ levels. Moreover, the $j$ = 0 $\leftarrow$ 1 subband is overlapped by strong (C$_2$D$_2$)$_2$ transitions. We use a term value approach, obtaining a self-consistent set of experimental" energy levels which can be directly compared with theory or fitted in terms of a Coriolis model. Challenges also arise with Ne-C$_2$D$_2$, which is not quite so close to the free rotor limit, but still has many overlapping lines. Insights gained here help in assigning the tricky $R(1)$ region for Ne-C$_2$D$_2$. Issue Date: 2014-06-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: McKellar, B.; Moazzen-Ahmadi, N. PROGRESS IN UNDERSTANDING THE INFRARED SPECTRA OF He- AND Ne-C2D2. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.FB08 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/50769 DOI: https://doi.org/10.15278/isms.2014.FB08 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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