J/ApJ/783/77 Line lists of transitions for interstellar urea (Remijan+, 2014)
Observational results of a multi-telescope campaign in search of interstellar
urea [(NH2)2CO].
Remijan A.J., Snyder L.E., McGuire B.A., Kuo H.-L., Looney L.W.,
Friedel D.N., Golubiatnikov G.Y., Lovas F.J., Ilyushin V.V., Alekseev E.A.,
Dyubko S.F., McCall B.J., Hollis J.M.
<Astrophys. J., 783, 77 (2014)>
=2014ApJ...783...77R 2014ApJ...783...77R (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Atomic physics
Keywords: astrochemistry - ISM: clouds - ISM: individual (Sagittarius B2(N)) -
ISM: molecules
Abstract:
In this paper, we present the results of an observational search for
gas phase urea [(NH2)2CO] observed toward the Sgr B2(N-LMH)
region. We show data covering urea transitions from ∼100GHz to 250GHz
from five different observational facilities: the
Berkeley-Illinois-Maryland-Association (BIMA) Array, the Combined
Array for Research in Millimeter-wave Astronomy (CARMA), the NRAO 12m
telescope, the IRAM 30m telescope, and the Swedish-ESO Submillimeter
Telescope (SEST). The results show that the features ascribed to urea
can be reproduced across the entire observed bandwidth and all
facilities by best-fit column density, temperature, and source size
parameters which vary by less than a factor of two between
observations merely by adjusting for telescope-specific parameters.
Interferometric observations show that the emission arising from these
transitions is cospatial and compact, consistent with the derived
source sizes and emission from a single species. Despite this
evidence, the spectral complexity of both (NH2)2 CO and of Sgr
B2(N) makes the definitive identification of this molecule
challenging. We present observational spectra, laboratory data, and
models, and discuss our results in the context of a possible molecular
detection of urea.
Description:
The first measurements of the microwave spectra of urea were made from
5GHz to 50GHz using a heated waveguide cell (Brown et al.,
1975JMoSp..58..445B 1975JMoSp..58..445B). Further measurements were reported by Kasten &
Dreizler (1986ZNatA..41.1173K 1986ZNatA..41.1173K) and Kretschmer et al.
(1996MolPh..87.1159K 1996MolPh..87.1159K). New spectroscopic measurements were made at
NIST over the frequency range from 59GHz to 114GHz. A total of 38
rotational transitions was measured. Later, the Kharkov group carried
out higher frequency measurements. Using a heated quartz absorption
cell utilizing an automated synthesizer-based spectrometer (Ilyushin
et al., 2005JMoSp.231...15I 2005JMoSp.231...15I), the Kharkov group provided 75 new
measurements between 78GHz and 240GHz. The urea lines for which we
searched were calculated using the millimeter-wave data discussed
above, as well as the hyperfine-free data from the existing literature
cited earlier.
As an aid to further interstellar searches for urea transitions, we
provide a complete list of predicted rotational lines of urea
available in Table6 covering the frequency range of 1GHz to 600GHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 72 4120 Measured and calculated frequencies and associated
spectroscopic constants of urea [(NH2)2CO]
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See also:
http://www.cv.nrao.edu/php/splat/ : Splatalogue database for astronomical
spectroscopy
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 F10.3 MHz Freq1 [1111.6/599859.1] Calculated Frequency
12- 15 I4 MHz e_Freq1 [0/4255] The 2σ uncertainty in Freq (1)
17- 26 F10.3 MHz Freq2 [5816.6/232837]? Measured Frequency
28- 30 I3 MHz e_Freq2 [1/500]? The 2σ uncertainty in MFreq (1)
32- 38 F7.3 cm-1 Elow [0/604.771] Lower state energy level
40- 42 I3 --- J1 [1/40] J quantum number of the upper state (J')
44- 45 I2 --- Ka1 [0/40] Ka quantum number of the upper state
(K'a)
47- 48 I2 --- Kc1 [0/40] Kc quantum number of the upper state
(K'c)
50- 52 I3 --- J0 [0/40] J quantum number of the lower state (J'')
54- 55 I2 --- Ka0 [0/39] Ka quantum number of the lower state
(K''a)
57- 58 I2 --- Kc0 [0/40] Kc quantum number of the lower state
(K''c)
60- 66 F7.4 --- Sij [0/39.5] Transition line strength
68- 72 A5 --- Ref Reference (2)
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Note (1): In units of the last digit and are of type A (coverage factor k=2)
(Taylor & Kuyatt 1994, Guidelines for Evaluation and Expressing the
Uncertainty of NIST Measurement Results (NIST Tech. Note 1297)
(Washington, DC: GPO)).
Note (2): Reference codes are defined as follows:
Bro75 = Brown et al. (1975JMoSp..58..445B 1975JMoSp..58..445B);
Gol01 = NIST spectroscopic measurement;
Ily05 = Ilyushin et al. (2005JMoSp.231...15I 2005JMoSp.231...15I). This flag was "Ily03" in the
MRT original table of the paper and was corrected in Ily05 at CDS.
Kas86 = Kasten & Dreizler (1986ZNatA..41.1173K 1986ZNatA..41.1173K);
Kre96 = Kretschmer et al. (1996MolPh..87.1159K 1996MolPh..87.1159K).
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 15-Apr-2016