CH3CH2NH2 - University of Arizona

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The Astrophysical Journal, 673:1240–1248, 2008 February 1 # 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.

THE ROTATIONAL SPECTRUM OF ANTI-ETHYLAMINE (CH3CH2NH2) FROM 10 TO 270 GHz: A LABORATORY STUDY AND ASTRONOMICAL SEARCH IN SGR B2(N) A. J. Apponi, M. Sun, D. T. Halfen,1 and L. M. Ziurys Departments of Chemistry and Astronomy, LAPLACE Center for Astrobiology, Arizona Radio Observatory, Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ, 85721

and H. S. P. Mu¨ller I. Physikalisches Institut, Universita¨t zu Ko¨ln, Zu¨lpicher Strasse 77, 50937, Cologne, Germany Received 2007 July 25; accepted 2007 September 10

ABSTRACT The pure rotational spectrum of the lowest energy (anti-) conformer of ethylamine (CH3CH2NH2) has been measured in the frequency range of 10–270 GHz. The spectrum was recorded using both millimeter-wave absorption spectroscopy and Fourier transform microwave (FTMW ) techniques. Ten rotational transitions of this molecule were recorded in the frequency range of 10–40 GHz using FTMW methods, resulting in the assignment of 53 quadrupoleresolved hyperfine lines; in the millimeter-wave region (48–270 GHz), nearly 600 transitions were assigned to the ground (anti-) state. The amine group in CH3CH2NH2 undergoes inversion, resulting in a doubling that is frequently small and most apparent in the low-frequency K-doubling transitions. In addition, seemingly random rotational levels of this molecule were found to be significantly perturbed. The cause of these perturbations is presently uncertain, but torsion-rotation interactions with the higher lying gauche conformers seem to be a likely explanation. An astronomical search was conducted for ethylamine toward Sgr B2( N ) using the Kitt Peak 12 m antenna and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory. Frequencies of 70 favorable rotational transitions were observed in this search, which covered the range 68–263 GHz. Ethylamine was not conclusively detected in Sgr B2(N ), with an upper limit to the column density of (1 8) ; 1013 cm
2 with f (CH3 CH2 NH2 /H2 )  (0:3 3) ; 10
11 , assuming a rotational temperature of 50–220 K. These observations indicate a gas-phase CH3 CH2 NH2 /CH3 NH2 ratio of