J/ApJ/812/L5 CH3NCO (methyl isocyanate) transition frequencies (Halfen+, 2015)
Interstellar detection of methyl isocyanate CH3NCO in Sgr B2(N):
a link from molecular clouds to comets.
Halfen D.T., Ilyushin V.V., Ziurys L.M.
<Astrophys. J., 812, L5 (2015)>
=2015ApJ...812L...5H 2015ApJ...812L...5H (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Interstellar medium ; Spectra, millimetric/submm
Keywords: astrochemistry; comets: individual: 67P&Churyumov-Gerasimenko;
ISM: molecules; line: identification; methods: laboratory: molecular;
molecular data
Abstract:
A new interstellar molecule, CH3NCO (methyl isocyanate), has been
detected using the 12m telescope of the Arizona Radio Observatory
(ARO). CH3NCO was identified in spectra covering 48GHz (68-116GHz)
in the 3mm segment of a broadband survey of Sgr B2(N). Thirty very
favorable rotational lines (Ka=0 and Ka=1 only; Eu<60K)
originating in five consecutive transitions (J=8->7, 9->8, 10->9,
11->10, and 12->11) in both the A and E internal rotation species are
present in this frequency range. Emission was observed at all of the
predicted frequencies, with 17 lines appearing as distinct,
uncontaminated spectral features, clearly showing the classic a-type,
asymmetric top pattern, with TR*∼20-70mK. The CH3NCO spectra
also appear to exhibit two velocity components near VLSR∼62 and
73km/s, both with ΔV1/2∼10km/s --typical of molecules such as
CH2CHCN, HNCO, and HCOOCH3 in Sgr B2(N). The column density of
CH3NCO in Sgr B2(N) was determined to be Ntot∼2.3x1013 and
1.5x1013/cm2 for the 62 and 73km/s components, corresponding to
fractional abundances, relative to H2, of f∼7.6x10-12 and
5.0x10-12, respectively. CH3NCO was recently detected in volatized
material from comet 67P/Churyumov-Gerasimenko by Rosetta's Philae
lander, with an abundance ∼1.3% of water; in Sgr B2(N), CH3NCO is
roughly ∼0.04% of the H2O abundance.
Description:
In order to establish accurate rest frequencies in the 3mm window,
which lies above 40GHz, we conducted a new analysis of CH3NCO using
the previous data of Koput (1986JMoSp.115..131K 1986JMoSp.115..131K) and new spectra
measured in the Ziurys laboratory in the 60-88GHz range with the FTmmW
spectrometer. See table 1 and section 2 for further details.
Observations of CH3NCO were performed as part of the spectral survey
of Sgr B2(N). The data were collected during 2002 September-2014 March
using the ARO 12m telescope on Kitt Peak, Arizona, and the
Submillimeter Telescope (SMT) on Mount Graham.
Objects:
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RA (ICRS) DE Designation(s)
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17 47 19.3 -28 22 22 Sgr B2(N) = NAME SGR B2(N)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 42 97 Previous and new rest frequencies of CH3NCO (vb=0)
of the revised analysis
table3.dat 131 45 Observed parameters for CH3NCO in Sgr B2(N)
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See also:
J/A+A/566/L5 : C/2012 F6 (Lemmon) & C/2013 R1 spectra (Lovejoy) (Biver+, 2014)
J/A+A/559/A47 : Sgr B2(N) and Sgr B2(M) IRAM 30m line survey (Belloche+, 2013)
J/ApJ/724/994 : Cyano- to methanol and ammonia observations (Braakman+, 2010)
J/A+A/455/971 : Organic molecules in Galactic center (Requena-Torres+, 2006)
J/ApJS/158/188 : Detection of glycolaldehyde toward Sgr B2 (Widicus+, 2005)
J/ApJS/117/427 : Sgr B2 spectral survey (Nummelin+, 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- J1 [1/12] Upper J quantum number
4- 5 I2 --- Ka1 [-3/3] Upper Ka quantum number
7- 8 I2 --- Kc1 [1/12] Upper Kc quantum number
10- 11 I2 --- J0 [0/11] Lower J quantum number
13- 14 I2 --- Ka0 [-3/3] Lower Ka quantum number
16- 17 I2 --- Kc0 [0/11] Lower Kc quantum number
19 A1 --- A/E [AE] A/E symmetry
21- 22 I2 --- m [-3/4] Internal rotation quantum number, m
24- 33 F10.3 MHz Freq [8671.3/104999] Frequency of the transition
35- 40 F6.3 MHz O-C [-2/1.3] Observed minus calculated value
42 A1 --- r_Freq [ab] Source of frequency (1)
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Note (1): Below 40GHz, frequencies from Koput (1986JMoSp.115..131K 1986JMoSp.115..131K).
Above 40GHz, from this work, unless specified as follows:
a = From Kasten & Dreizler (1986ZNatA..41..637K 1986ZNatA..41..637K).
b = Estimated from observed spectra in Figure 1.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Trans Transition J'Ka,Kc->J"Ka,Kc
22 A1 --- A/E [AE] A/E symmetry
24 I1 --- m [0/1]? Internal rotation quantum number, m
26- 35 F10.3 MHz Freq [68536.7/105000.3]? Frequency of the transition
37- 41 F5.3 MHz e_Freq [0.005/1.2]? Freq uncertainty
43- 47 F5.2 K Eu [14.9/57.5]? Upper state energy
49- 53 F5.2 D2 mu2S [63/98.6]? Line strength (µ2S)
55- 58 F4.2 --- etac [0.8/1]? Corrected beam efficiency ηc
60- 61 I2 arcsec theta [60/92]? θb value
63 A1 --- l_TR* [~] Uncertainty flag on TR*
65- 69 F5.3 K TR* [0.01/0.08]? Temperature scale (1)
71- 75 F5.3 K e_TR* [0.002/0.005]? TR* uncertainty
77 A1 --- l_DelV12 [~] Uncertainty flag on DelV12
79- 80 I2 km/s DelV12 [10/22]? Difference between the two
velocity components (ΔV1/2)
82 I1 km/s e_DelV12 [2/4]? DelV12 uncertainty
84 A1 --- u_Vlsr [~] Uncertainty flag on Vlsr
86- 87 I2 km/s Vlsr [62/73]? LSR velocity
89 I1 km/s e_Vlsr [2/4]? Vlsr uncertainty
91 A1 --- f_Vlsr [a] Flag on Vlsr
93-131 A39 --- Comm Comment
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Note (1): The temperature scale was established using the chopper wheel method,
corrected for forward spillover losses, and given as TR*.
The radiation temperature TR is then TR=TR*/ηc, where
ηc is the corrected beam efficiency. See section 3.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Feb-2016