The complete rotational spectrum of CH 3 NCO up to 376 GHz Zbigniew Kisiel, a Lucie Kolesnikova, b Jose L. Alonso, b Ivan R. Medvedev, c Sarah Fortman, d Manfred Winnewisser, d Frank C. De Lucia d a Institute of Physics, Polish Academy of Sciences, Warszawa, Poland b Grupo de Espectroscopia Molecolar, Lab. De Espectroscopia y Bioespectroscopia, Unidad Asociada CSIC, Universidad de Valladolid, Valladolid, Spain c Department of Physics, Wright State University, Dayton, OH, USA d Department of Physics, The Ohio State University, Columbus, OH, USA 70th International Symposium on Molecular Spectroscopy TG08

Previous work: Curl et al., J.Chem.Phys. 39,3335(1963)  = 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)V 3 = 29(5) cm -1,  aa = +2.86(3) MHz J.Koput, J.Mol.Spectrosc. 115,131(1986)Comprehensive analysis up to J=4  3, V bend =928(5) cm -1, V 3 =20.7(1) cm -1 Kasten+Dreizler, Z.Naturf. A 41,637(1986)    D,  aa = (8) MHz Kisiel et al., RC10, 65th Symposium (2010)FASSST spectrum over GHz, series analysis with J(J+1) expansions Assignment ? Fits ? New stimulus…   = 180 –  (CNC)

CNC bending potentials: cm  CH 3 NCS, Koput, J.Mol.Spectrosc. 118,189 (1986) CH 3 NCO, Koput, J.Mol.Spectrosc. 115,131 (1986) v b =  /deg   = 180 –  (CNC) greater  b and V b smaller V 3

The complete rotational spectrum of CH 3 NCO: FASSST GHz VDI sources GHz Stark GHz Simulated 8-39 GHz, from the Koput linelist (1986) + supersonic expansion chirped pulse 8-18 GHz Single spectrum compiled with the SVIEW_L program from Single spectrum compiled with the SVIEW_L program from AABS

Some problems: J” = No experimental relative intensities Stark spectroscopy was carried out last and faced serious sample decomposition problems Inconsistent relative intensities, spurious harmonics

Loomis-Wood assignment of K a = 0 transitions: v b =1, m=0, K= 0 v b =0, m=0, K= 0 J” J’

Loomis-Wood assignment of K a = 5 transitions: J” J’

Loomis-Wood assignment of K a = 10 transitions: ? J” J’

The need for complete data: J” J’

Reproduction of the spectrum by assigned sequences: The J = 12  11 transition of CH 3 NCO Spectrum Sequences ? ? ? ? ?

CONCLUSIONS: Dedicated program written to keep track of the fitted sequences + higher terms ?

Current assignment: v b =0, m=0, K= 110v b =0, m=1, K= Frequencies of all g.s. lines up to K a =3 and 360 GHz have been measured experimentally

The fitting tool ? Watson’s Hamiltoniam 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) Toluene ground state ( m = 0 )

The value D J for CH 3 NCO: D J /kHz Unscaled B3LYP/6-31G(d,p): 1.98 Histogram of the effective D J values from over 220 empirical sequences Effective values:2.15(10) RAM36 fit to g.s. K a =0,1,2:2.2221(16)

 The new GHz measurements allow the transitions in the FASSST spectrum to be unambiguously connected to the centimeter-wave, low-J sequences assigned by Stark spectroscopy.  The K assignment can now be extended beyond K=3.  The assigned g.s. sequences provide a complete set of experimental frequencies that can be used in astrophysics.  The GHz spectrum is currently reduced to about 230 different line sequences using power series of J(J+1) and can be reconstructed from fitted values of B eff, D eff, H eff, … + experimental relative intensity.  Application of RAM36 holds promise for fitting (low barier) internal rotation. „There seems to be (as yet) little value in reporting values of the constants or details of the fits” but soon there might be ….SUMMARY: