J/ApJ/805/141 Transition frequencies of MN and DMN (Schnitzler+, 2015)
High-resolution Fourier-transform microwave spectroscopy of methyl- and
dimethylnapthalenes.
Schnitzler E.G., Zenchyzen B.L.M., Jager W.
<Astrophys. J., 805, 141 (2015)>
=2015ApJ...805..141S 2015ApJ...805..141S (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Radio lines
Keywords: astrochemistry; ISM: molecules; molecular data
Abstract:
High-resolution pure rotational spectra of four alkylnaphthalenes were
measured in the range of 6-15GHz using a molecular-beam
Fourier-transform microwave spectrometer. Both a- and b-type
transitions were observed for 1-methylnaphthalene (1-MN),
1,2-dimethylnaphthalene (1,2-DMN), and 1,3-dimethylnaphthalene
(1,3-DMN); only a-type transitions were observed for
2-methylnaphthalene (2-MN). Geometry optimization and vibrational
analysis calculations at the B3LYP/6-311++G(d,p) level of theory aided
in the assignments of the spectra and the characterization of the
structures. Differences between the experimental and predicted
rotational constants are small, and they can be attributed in part to
low-lying out-of-plane vibrations, which distort the alkylnaphthalenes
out of their equilibrium geometries. Splittings of rotational lines
due to methyl internal rotation were observed in the spectra of 2-MN,
1,2-DMN, and 1,3-DMN, and allowed for the determination of the
barriers to methyl internal rotation, which are compared to values
from density functional theory calculations. All four species are
moderately polar, so they are candidate species for detection by radio
astronomy, by targeting the transition frequencies reported here.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 36 48 Measured transition frequencies of
1-methylnaphthalene (1-MN)
table5.dat 45 78 Measured transition frequencies of
2-methylnaphthalene (2-MN)
table6.dat 45 70 Measured transition frequencies of
1,3-dimethylnaphthalene (1,3-DMN)
table7.dat 45 147 Measured transition frequencies of
1,2-dimethylnaphthalene (1,2-DMN)
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See also:
J/ApJ/662/1309 : Rotational spectra of small PAHs (Thorwirth+, 2007)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1 I1 --- J1 [3/9] Upper quantum number J
3 I1 --- Ka1 [0/4] Upper quantum number Ka
5 I1 --- Kc1 [0/9] Upper quantum number Kc
7 I1 --- J0 [2/8] Lower quantum number J
9 I1 --- Ka0 [0/4] Lower quantum number Ka
11 I1 --- Kc0 [0/8] Lower quantum number Kc
13- 22 F10.4 MHz Freq [7869.7/13573.7] Experimental transition frequency
24- 30 F7.4 MHz O-C [-0.003/0.002] Residual
32- 36 F5.3 --- S [0.7/8.8] Transition line strength
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Byte-by-byte Description of file: table[567].dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- J1 [5/12] Upper quantum number J
4 I1 --- Ka1 [0/4] Upper quantum number Ka
6- 7 I2 --- Kc1 [2/11] Upper quantum number Kc
9- 10 I2 --- J0 [4/12] Lower quantum number J
12 I1 --- Ka0 [0/4] Lower quantum number Ka
14- 15 I2 --- Kc0 [1/10] Lower quantum number Kc
17- 19 A3 --- State [AE' ] Symmetry component (1)
21- 30 F10.4 MHz Freq [6596.3/14721.9] Experimental transition frequency
32- 38 F7.4 MHz O-C [-0.03/0.03] Residual
40- 45 F6.3 --- S [2.4/10.9] Transition line strength
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Note (1): For 2-MN (see Figure 3) and 1,3-DMN (see Figure 4), methyl internal
rotation splittings were observed, so two pairs of Doppler components,
corresponding to the A and E symmetry components, were detected for
each transition.
For 1,2-DMN (see Figure 5), additional splittings due to internal
rotation of both methyl substituents occurred, resulting in five fine
structure components with symmetry labels AA, AE, EA, EE, and EE'.
See section 3.1 for further explanations.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Emmanuelle Perret [CDS] 16-Sep-2015