Experimental Molecular Emission Spectroscopy of Ethylene Oxide in ALMA Band 6A. Tamanai,1 Y. Watanabe,2 T. Sakai,3 R. Nakatani,1 S. Zeng,1 S. Yamamoto,4 and N. Sakai1
1 Cluster for Pioneering Research, RIKEN, Japan
2Material Science and Engineering, Shibaura Institute of Technology, Japan
3Department of Engineering Science, The University of Electro-Communications, Japan
4Department of physics, The University of Tokyo, Japan

New discoveries related to astrochemistry in mm and sub-mm frequency ranges haveprovided us fruitful information on valuable chemical properties of organic compounds.
Thanks to the highly sensitive ALMA telescope, it has become possible to detect very
complex interstellar organic molecules than ever before [1-4]. Emission and absorption lines
from each molecule obtained from observations give us a clue to understand the chemical
pathways from simple molecules to complex molecules including the essential molecules oflife.
Either or both of theoretically calculated and experimentally measured emission spectra areapplied for interpretation of observed molecular lines in general. One of major problems
concerning molecular survey is that an insufficient supply of experimentally measured data
sets for both organic and inorganic compounds in millimeter and submillimeter frequency
ranges. To solve this problem, we have set up the emission type molecular spectroscope forastronomically relevant materials in the frequency range between 216 GHz and 264 GHz(ALMA Band 6). Superconductor-Insulator-Superconductor (SIS) mixer for ~230 GHz band
mounted on the ALMA-type cartridge receiver as a heterodyne apparatus (SUMIRE) isapplied in this measurement (details in [3]).
In here, we introduce our experimental broadband and high-resolution spectroscopic
apparatus as well as a measured ethylene oxide (C 2H4O) which has been detected in highmass star forming regions such as the galactic center source Sgr B2 (N) [5], hot molecular
clouds DR21 (OH), NGC7538 [6] and low-mass protostar IRAS 16293-2422 [7]. In
consequence, 677 peaks due to rotational transitions have been detected. Molecularparameters including predicted transition frequencies, rotational constants, and centrifugal
distortion constants were derived by making use of a least-squares analysis and selfdeveloped SUMIRE data analysis code, Aqualious for both C2H4O and 13C2H4O. 256 peaks
and 108 peaks were assigned as contributions from C2H4O and 13C2H4O rotational transitions,respectively. In addition, we compared our experimental outcomes with the data sets in
Cologne Database for Molecular Spectroscopy (CDMS) [8] and previous works [9-10].
Thereby our results are in good agreement with previously obtained data. This also
demonstrates the reliability of our experimental results.
References
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[8][9][10]

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