1. Further analysis of the laboratory rotational spectrum of CH3NCO
71st International Symposium on Molecular Spectroscopy WF07
Further analysis of the laboratory rotational spectrum of CH3NCO
Zbigniew Kisiel,a Lucie Kolesnikova,b Jose L. Alonso,b
Manfred Winnewisser,c Frank C. De Lucia,c Ivan Medvedev,d Belen Tercero,e
Jose Cernicharo,e Jean-Claude Guillemin,f
aInstitute of Physics, Polish Academy of Sciences, Warszawa, Poland
bGrupo de Espectroscopia Molecolar, Lab. De Espectroscopia y Bioespectroscopia,
Unidad Asociada CSIC, Universidad de Valladolid, Valladolid, Spain
cDepartment of Physics, The Ohio State University, Columbus, OH, USA
dDepartment of Physics, Wright State University, Dayton, OH, USA
eDepartmento de Astrofisica, Centro de Astrobiologia CAB, Madrid, Spain
f Institut des Sciences Chimiques de Rennes, Rennes, France

2. Praha2008
Previous work: r
1/ nearly free internal rotation of the CH3 group:
V3=20.7(1) cm-1
2/ CNC bending motion:
Vbend=928(5) cm-1 E(b=1-0)=182 cm-1
Curl et al., J.Chem.Phys. 39,3335(1963) m = 2.81(6)D, aa = +2.3 MHz
„There seems to be little value in reporting
values of the constants or details of the fits”
Lett+Flygare, J.Chem.Phys. 47,4730(1967), Kasten+Dreizler, Z.Naturf. A 41,637(1986)
J.Koput, J.Mol.Spectrosc. 115,131(1986) Comprehensive analysis up to J=4  3
Kisiel et al., RC10, 65th Symposium (2010) series analysis with J(J+1) expansions
Kisiel et al., TG08, 70th Symposium (2015) of complete experimental spectrum to
363 GHz
Pondering on a new fit when…

4. Analysis of the COSAC mass spectrum:
Goesmann et al., “Organic compounds on coment 67P/Churyumov-Gerasomenko revealed by COSAC mass spectrometry” Science 349 (31 July 2015)
COSAC = COmetary SAmpling and Composition experiment

5. Series analysis:
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Each (vb, m, K) line series fitted with an individual J(J+1) expansion
Dedicated program written to keep track of the fitted sequences
Line lists to well over 300 GHz constructed from experimental frequencies (augmented by interpolated values when necessary)
from Table A.1 of A&A 587, L4 (2016):

6. Praha2008
Astrophysical identification even with tools of laboratory spectroscopy:
Loomis-Wood display of ALMA Science Verification observations J”
242.1 GHz 27
241.7 GHz 26 25
216.3 GHz 24
215.9 GHz
m = 0
K = 0
K = 3L

7. Spatial distribution in Orion:
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plenary talk RA04 by Jose Cernicharo

8. A limited, effective asymmetric rotor fit is possible:
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see Table A.2 A&A 587, L4 (2016)
Quartics are compatible with ab initio

9. 14N nuclear quadrupole splitting in parent CH3NCO:
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14N nuclear quadrupole splitting in parent CH3NCO:
Recorded in supersonic expansion
NOTES:
Koput gives hyperfine removed frequencies in J.Mol.Spectrosc. 115, 131 (1986)
For hyperfine frequencies up to 78GHz and K 2 see Table A.8 A&A 587, L4 (2016)
The full line-list in Table A5 is also hyperfine-free, but splitting mostly not relevant above GHz.

10. Partition function:
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SPCAT summation to Evib =402 cm-1 involves 18 vibrational substates !

11. Partition function: ratio = 7.8 ratio = 4.0
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Partition function:
Sensitivity to summation conditions
ratio = 7.8
ratio = 4.0

12. Stark assignment of K > 3 transitions:
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Stark assignment of K > 3 transitions:
From Stark spectra recorded at electric field of 5 V/cm
m = 0, J = 5 ← 4, K= 3
M =
m = ?, J = 5 ← 4, K= 4
M =

13. Praha2008
13CH3NCO
and
CH3N13CO

14. 13C species were synthesised at excellent isotopic purity:
Praha2008
13C species were synthesised at excellent isotopic purity:
Stark spectra of the J = 6  5 transition recorded at electric field of 5 V/cm
m=0, K= 2
m=-2, K= ±1

15. * CH3N13CO: spectrum remarkably similar to that of the parent
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CH3N13CO: spectrum remarkably similar to that of the parent
This 13C is only 0.63Å from the centre of mass
J = 6  5 transition
170 MHz isotopic shift *

16. Praha2008
13CH3NCO: 13C is now 1.85Å from the c.m. and the isotopic spectrum is shifted
by 1440 MHz
Similarities are now outnumbered by differences
J = 6  5 transition ? *

17. 13C lines also found assignable in the FASSST spectrum from OSU:
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13CH3NCO
CH3N13CO
GHz J”
GHz

18. Series analysis for 13C passes checks against the parent:
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Series analysis for 13C passes checks against the parent:
Ka seqnce Irel Nin Nrej RMS B /MHz DJ /kHz ....
vb=0, m=0 (gs) E_vib = 0 cm-1
0 V093: (13) (43)
V093: (14) (41)
V093: (15) (29)
1L V126: (10) (21)
V126: (20) (39)
V126: (19) (35)
1U V131: (14) (30)
V131: (14) (27)
V131: (25) (52)
2L V089: (82) (94)
V089: (79) (95)
V089: (11) (16)
2U V006: (16) (56)
V006: (84) (10)
V006: (19) (50)
parent
CH3N13CO
13CH3NCO

19. Fit to experimental accuracy and encompassing more than
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Fit to experimental accuracy
and encompassing more than
m = 0, Ka ≤ 2 ?

20. The fitting tool ? Toluene ground state ( m = 0 )
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Toluene ground state ( m = 0 )
Watson’s Hamiltonian using ASFIT
Kisiel et al., J.Mol.Spectrosc. 227,109(2004)
Torsion-rotation Hamiltonian using RAM36
Ilyushin et al., J.Mol.Spectrosc. 259,26(2010)
Ilyushin et al., J.Mol.Spectrosc. 267,186(2011)

21. The m=0 (ground state) problems in CH3NCO:
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K = 4 ?
K = 5 ? ….

22. The m=1 problem in CH3NCO :
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K = 0 !

23. The perils of using a small data set:
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Frequency /MHz
see Table A7 of Cernicharo, Kisiel, Tercero et al., A&A 587, L4 (2016)

24. Praha2008
SUMMARY:
Last year’s statement that „The assigned sequences provide a complete set of experimental frequencies that can be used in astrophysics„ has been consummated: hundreds of lines assigned in Orion and line list with 1300 frequencies published
New Stark measurements allow the K assignment to be extended beyond K=3, but confident m assignment still requires a spectroscopic fit
Analysis based on sequences now extended to 13CH3NCO and CH3N13CO
The challenge of a better (global fit) remains and RAM36 still seems the best tool although the fit is still far from trivial…
R.F.Curl:
„There seems to be (as yet) little value in reporting values of the constants
or details of the fits” ….
but:
basic spectral information for astrophysics now in A&A 587, L4 (2016)

25. Table A7 of Cernicharo, Kisiel, Tercero et al., A&A 587, L4 (2016)
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