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

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…

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

Series analysis: Praha2008 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):

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

Spatial distribution in Orion: Praha2008 plenary talk RA04 by Jose Cernicharo

A limited, effective asymmetric rotor fit is possible: Praha2008 see Table A.2 A&A 587, L4 (2016) Quartics are compatible with ab initio

14N nuclear quadrupole splitting in parent CH3NCO: Praha2008 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 60-70 GHz.

Partition function: Praha2008 SPCAT summation to Evib =402 cm-1 involves 18 vibrational substates !

Partition function: ratio = 7.8 ratio = 4.0 Praha2008 Partition function: Sensitivity to summation conditions ratio = 7.8 ratio = 4.0

Stark assignment of K > 3 transitions: Praha2008 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 = 4 3 2 1 m = ?, J = 5 ← 4, K= 4 M = 4 3 2 1

Praha2008 13CH3NCO and CH3N13CO

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

* CH3N13CO: spectrum remarkably similar to that of the parent Praha2008 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 *

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 ? *

13C lines also found assignable in the FASSST spectrum from OSU: Praha2008 13CH3NCO CH3N13CO GHz J” GHz 343.7 40 352.3 302.2 35 309.7 260.5 30 267.0 218.7 25 224.2

Series analysis for 13C passes checks against the parent: Praha2008 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: 0.843 41 1 0.910 4335.6996(13) 8.4815(43) V093: 0.865 36 0 0.735 4321.7180(14) 8.4036(41) V093: 0.611 37 0 1.243 4215.8348(15) 7.8872(29) 1L V126: 0.783 38 2 0.967 4297.6203(10) 3.3744(21) V126: 0.880 25 0 0.868 4283.8567(20) 3.3430(39) V126: 1.000 28 0 1.315 4179.5075(19) 3.1850(35) 1U V131: 0.786 38 2 1.249 4376.1857(14) 4.2752(30) V131: 0.934 23 0 0.499 4361.9797(14) 4.2485(27) V131: 0.873 24 0 1.200 4254.5237(25) 4.0348(52) 2L V089: 0.761 38 1 1.101 4339.69609(82) 3.28715(94) V089: 0.777 29 0 0.791 4325.71195(79) 3.26547(95) V089: 0.628 26 0 0.989 4219.7976(11) 3.1158(16) 2U V006: 0.835 38 1 1.046 4339.6811(16) -2.8764(56) V006: 0.748 29 0 0.841 4325.69873(84) -2.8289(10) V006: 0.845 26 0 1.004 4219.7850(19) -2.5665(50) parent CH3N13CO 13CH3NCO

Fit to experimental accuracy and encompassing more than Praha2008 Fit to experimental accuracy and encompassing more than m = 0, Ka ≤ 2 ?

The fitting tool ? Toluene ground state ( m = 0 ) Praha2008 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)

The m=0 (ground state) problems in CH3NCO: Praha2008 K = 4 ? K = 5 ? ….

The m=1 problem in CH3NCO : Praha2008 K = 0 !

The perils of using a small data set: Praha2008 Frequency /MHz see Table A7 of Cernicharo, Kisiel, Tercero et al., A&A 587, L4 (2016)

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)

Table A7 of Cernicharo, Kisiel, Tercero et al., A&A 587, L4 (2016) Praha2008