J/A+A/568/A58 HCOO13CH3 rotational spectrum (Haykal+, 2014)
THz spectroscopy and first ISM detection of excited torsional states
of 13C-methyl formate.
Haykal I., Carvajal M., Tercero B., Kleiner I., Lopez A., Cernicharo J.,
Motiyenko R.A., Huet T.R., Guillemin J.C., Margules L.
<Astron. Astrophys. 568, A58 (2014)>
=2014A&A...568A..58H 2014A&A...568A..58H
ADC_Keywords: Interstellar medium ; Atomic physics ; Radio lines
Keywords: line: identification - astronomical databases: miscellaneous -
ISM: molecules - submillimeter: ISM - astrochemistry -
ISM: individual objects: Orion KL
Abstract:
An astronomical survey of interstellar molecular clouds needs a
previous analysis of the spectra in the microwave and sub-mm energy
range of organic molecules to be able to identify them. We obtained
very accurate spectroscopic constants in a comprehensive laboratory
analysis of rotational spectra. These constants can be used to predict
the transitions frequencies very precisely that were not measured in
the laboratory.
We present the experimental study and its theoretical analysis for two
13C-methyl formate isotopologues to detect these two isotopologues
for the first time in their excited torsional states, which lie at
130/cm (200K) in Orion-KL.
New spectra of HCO-O-13CH3 (13C2) methyl formate were recorded
with the mm- and submm-wave spectrometer in Lille from 50 to 940GHz. A
global fit for vt=0 and 1 was accomplished with the BELGI program to
reproduce the experimental spectra with greater accuracy.
We analysed 5728 and 2881 new lines for vt=0 and 1 for
HCOO13CH3. These new lines were globally fitted with 846
previously published lines for vt=0. In consequence, 52 parameters
of the RAM Hamiltonian were accurately determined and the value of the
barrier height (V3=369.93168(395)/cm) was improved. We report the
detection of the first excited torsional states (vt=1) in Orion-KL
for the 13C2 and 13C1 methyl formate based on the present
analysis and previously published data. We provide column densities,
isotopic abundances, and vibrational temperatures for these species.
Following this work, accurate prediction can be provided. This permits
detecting 135 features of the first excited torsional states of
13C-methyl formate isotopologues in Orion-KL in the 80-280GHz
frequency range, without missing lines.
Description:
The details about synthesis and identification by NMR spectroscopy
were described in Carvajal et al. (2009, Cat. J/A+A/500/1109).
The millimeter- and submillimeter-wave spectra were recorded using the
Lille spectrometer that is based on solid-state sources. The sample
pressure was in the range 20-30x10-6 bars. Spectra were recorded at
room temperature (T=294K) in the 150-210, 225-315, 400-500, 500-630,
and 780-940GHz regions with frequency steps of 30, 36, 48, 54, and
76kHz and an acquisition time of 35ms per point. The absolute accuracy
of the line-centre frequency is estimated to be better than 30kHz
(50kHz above 700GHz) for isolated lines and can be as low as 100kHz
(150kHz above 700GHz) for blended or very weak lines. See section 2.2.
The IRAM spectra will be published on the IRAM website:
http://www.iram-institute.org/
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 113 9455 * 13C2-Methylformate HCO-O-13CH3 data
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Note on tablea1.dat: Assignments, observed frequencies, calculated frequencies,
residuals from the Rho-Axis Method (RAM) fit, line strengths, and lower energy
levels for 13C2-methyl formate (HCOO13CH3) microwave transitions from
vt=0 and vt=1 torsional states included in the fit with parameters of Table 2.
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See also:
J/A+A/500/1109 : Rotational spectrum of HCOO13CH3 (Carvajal+, 2009)
J/ApJ/714/1120 : Rotational spectrum and DCOOCH3 in Orion (Margules+, 2010)
J/ApJS/190/315 : Rotational spectrum of H13COOCH3 (Carvajal+, 2010)
J/A+A/538/A119 : 18O-methyl formate (HCO18OCH3) spectrum (Tercero+ 2012)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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3- 4 I2 --- vt' [0/1] Vibrational state (upper state)
7- 8 I2 --- J' [1/63] Quantum number (upper state)
10- 12 I3 --- Ka' [-35/35] Quantum number (upper state) (1)
15- 16 I2 --- Kc' [0/63] Quantum number (upper state)
18 A1 --- p' [±] Parity (upper state) (2)
21- 22 I2 --- vt'' [0/1] Vibrational state (lower state)
25- 26 I2 --- J'' [0/62] Quantum number (lower state)
28- 30 I3 --- Ka'' [-35/35] Quantum number (lower state) (1)
33- 34 I2 --- Kc'' [0/62] Quantum number (lower state)
36 A1 --- p'' [±] Parity (lower state) (2)
40- 49 F10.3 MHz Freq [4663/937370] Observed vt=0 and 1 microwave
transitions
51- 53 I3 kHz e_Freq [5/200] Uncertainty of Freq
58- 67 F10.3 MHz FreqC Calculated line frequency
70- 71 I2 kHz e_FreqC Uncertainty of FreqC
77- 82 F6.3 MHz O-C [-0.3/0.3] Residual (Observed minus calculated
frequencies value)
90- 96 F7.3 D+2 S [0/201.3] Calculated line strengths (S(i->f));
see section 4
98-106 F9.4 cm-1 Elow [0/1111] Lower energy levels for
13C2-methyl formate (HCOO13CH3) (3)
108-111 A4 --- Ref Reference of the data (AA09=Carvajal et al.,
2009, Cat. J/A+A/500/1109 or NEW=this work)
113 A1 --- Bl [B] B: blended lines
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Note (1): Levels of E species have a signed Ka value (Herbst et al.
1984JMoSp.108...42H 1984JMoSp.108...42H).
Note (2): Torsion-rotation levels of A species have a "parity" label.
Note (3): Lower state energy referred to the J=Ka=0 A-species energy level taken
as the zero of the energy (zero point torsional energy: 71.0704/cm).
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Acknowledgements:
Imane Haykal, Imane.Haykal (at) phlam.univ-lille1.fr
References:
Carvajal et al. Paper I. 2009A&A...500.1109C 2009A&A...500.1109C Cat. J/A+A/500/1109
Kleiner et al. Asymmetric-top molecules containing one methyl-like internal
rotor: Methods and codes for fitting and predicting spectra.
2010, J. Mol. Spectrosc., 260, 1
(End) Imane Haykal [PHLAM], Emmanuelle Perret [CDS] 20-Aug-2014