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Title:ROTATIONAL SPECTROSCOPY OF THE LOW ENERGY CONFORMER OF 2-METHYLBUTYRONITRILE AND SEARCH FOR IT TOWARD SAGITTARIUS B2(N2)
Author(s):Müller, Holger S. P.
Contributor(s):Menten, Karl M.; Belloche, Arnaud; Garrod, Robin T.; Grabow, Jens-Uwe; Schlemmer, Stephan; Lewen, Frank; Zingsheim, Oliver; Wehres, Nadine
Subject(s):Mini-symposium: ALMA's Molecular View
Abstract:
Quite recently, some of us detected \textit{iso}-propyl cyanide as the first branched alkyl molecule in space.\footnote{A. Belloche, R.~T. Garrod, H.~S.~P. M{\"u}ller, and K.~M. Menten, \textit{Science} \textbf{345} 1584.} The identification was made in an ALMA Cycle~0 and 1 molecular line survey of Sagittarius~B2(N) at 3~mm. The branched isomer was only slightly less abundant than its straight-chain isomer with a ratio of about 2\,:\,5. While initial chemical models favored the branched isomer somewhat, more recent models\footnote{R.~T. Garrod, A. Belloche, H.~S.~P. M{\"u}ller, and K.~M. Menten, \textit{Astron. Astrophys.}, in press; doi: 10.1051/0004-6361/201630254.} are able to reproduce the observed ratio. Moreover, the models predicted that among the next longer butyl cyanides (BuCNs) 2-methylbutyronitrile (2-MBN) should be more abundant than both $n$-BuCN and 3-MBN by factors of around 2, with $t$-BuCN being almost negligible._x000d_ _x000d_ With the rotational spectra of $t$- and $n$-BuCN studied,\footnote{Z. Kisiel, \textit{Chem. Phys. Lett.} \textbf{118} 134; M.~H. Ordu et al., \textit{Astron. Astrophys.} \textbf{541} A121.} we investigated those of 2-MBN and 3-MBN betwen $\sim$40 and $\sim$400~GHz by conventional absorption spectroscopy and by chirped-pulse and resonator Fourier transform microwave (FTMW) spectroscopy. The analyses were guided by quantum-chemical calculations._x000d_ _x000d_ Here we report the analysis of the low-energy conformer of 2-MBN and a search for it in our current ALMA data. Two additional conformers are higher by $\sim$250 and $\sim$280~cm$^{-1}$. The low-energy conformer displays a very rich rotational spectrum because of its great asymmetry ($\kappa \approx 0.14$) and large $a$- and $b$-dipole moment components. Accurate $^{14}$N quadrupole coupling parameters were obtained from the FTMW spectral recordings.
Issue Date:6/19/2017
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/97122
DOI:10.15278/isms.2017.MF03
Date Available in IDEALS:2017-07-27


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