Global analysis of broadband rotation and vibration-rotation spectra of sulfur dicyanide Zbigniew Kisiel, a Manfred Winnewisser, b Brenda P. Winnewisser, b Frank C. De Lucia, b Dennis W. Tokaryk, c Brant E. Billinghurst d a Institute of Physics, Polish Academy of Sciences, Warszawa, Poland b Department of Physics, The Ohio State University, Columbus, USA c Department of Physics, University of New Brunswick, New Brunswick, Canada d Canadian Light Source Inc., University of Saskatchewan, Saskatoon, Canada 68th OSU International Symposium on Molecular Spectroscopy RC04

Background: S(CN) 2 is a precursor to NCNCS, which is a quasilinear molecule with intriguing barrier crossing behaviour described by quantum monodromy, Winnewisser et al.: Phys.Rev.Lett. 95, (2005) J.Mol.Struct. 798, 1 (2006) PCCP 12, 8158 (2010) Work based so far relied on pure rotation transitions, and direct knowledge of vibrational energies is now required. The problem: no previous high resolution FIR spectra while both molecules have similar wavenumbers (120 and 80 cm -1 ) for the lowest bending mode. The solution: use the Bruker IFS 125HR at the CLS and initial (encouraging) results were reported at last year’s Symposium, talk TF01.

Results from the pure rotation FASSST spectrum: Extensive analysis of the GHz was reported in Kisiel et al., J.Mol.Spectrosc. 246, 39 (2007)

Spectra of S(CN) 2 recorded on the Bruker IFS 125HR at the CLS: v 4 : b-type band v 7 : a-type band v 8 : c-type (half) band

 4 = 1  0  4 = 2  1  4 = 3  2  4 = 4  3 Good visibility of v 4 hot-bands in the Loomis-Wood display:  4 = 5  4

The global fit of CLS and FASSST data for S(CN) 2 :  Pure rotational transitions in 12 different vibrational states = lines measured in the GHz FASSST spectrum  Rotation-vibration transitions in 7 different bands (3 fundamental and 4 hot bands) = 2005 lines measured in the CLS cm -1 spectrum  The triad and tetrad of perturbing states analysed in the FASSST spectrum now connected by rotation-vibration transitions  all data now in one fit  Weighted fit assumed 0.1 MHz and cm -1 measurement uncertainties AABSSPFIT/SPCAT PIFORM Data set set up with AABS, fits made with SPFIT/SPCAT and reformatted with PIFORM 24 per state on average

Automatic state-by-state fit statistics now possible with PIFORM : ( PIFORM is available at PISLIN I also recommend PISLIN

Obs. Calc. Reproduction of the S(CN) 2 v 4 b-type band using AABS : P-transition region indicator of transition present in the data set

Reproduction of the S(CN) 2 v 7 a-type band: Obs. Calc. Q-transition region

Blanking known lines in the v 4 region: original blanked

S(CN) 2 energies Infrared dark state (A 2 symmetry) only accessible via perturbations in pure rotational transitions in the FASSST spectrum (5) (5) (6) (6) (7) (22) (11) (12) (11) (7) (8) From global fit of FASSST+CLS data

(5) (6) (7) (8) (11) Comparison of fundamental wavenumbers with previous harmonic estimate: Kisiel et al., J.Mol.Spectrosc. 246, 39 (2007)

(5) (5) (6) (7) (22)  4   x 44   x 44   x 44   x 44 Evaluation of x 44 as a double check on vibrational energies:  x 44 = cm -1  x 44 = cm -1  x 44 = cm -1  x 44 = cm -1

Comparison with anharmonic force field calculation: Vibration-rotation changes in rotational constants (MHz): Fundamental wavenumbers (cm-1): CCSD(T)/aug-cc-pVTZ calculation made with CFOUR : 234 basis functions, 16.5 days on an i7 computer (NOTE: the B v -B 0 comparison is not yet unified, as exptal values are deperturbed, while CFOUR values are perturbation inclusive)

 High-resolution far-infrared spectra of the three lowest fundamentals of S(CN) 2 have been recorded at the CLS  Infrared and MMW measurements on 12 different vibrational states and 7 rotation-vibration bands were combined into one global fit  Precise vibrational energies were determined for 11 of the lowest excited vibrational states of S(CN) 2  Comparison of experimental B v -B 0 values with estimates from ab initio anharmonic calculation (made with CFOUR ) is encouraging and the r e SE geometry will be evaluated AABS  This problem stimulated the development of several different analysis tools, in particular of AABS, which now seems to be up to the challenge posed by this rather simple but synthetically temperamental molecule  Stay for the next talk for a report on the much more challenging NCNCS... CONCLUSIONS:

and: and: Special thanks: OSU International Symposium on Molecular Spectroscopy and the local organisers