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
Transcript
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. Billinghurstd
aInstitute of Physics, Polish Academy of Sciences, Warszawa, PolandbDepartment of Physics, The Ohio State University, Columbus, USA
cDepartment of Physics, University of New Brunswick, New Brunswick, CanadadCanadian Light Source Inc., University of Saskatchewan, Saskatoon, Canada
68th OSU International Symposium on Molecular Spectroscopy RC0468th 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.:
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 110-376 GHzwas 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:
v4: b-type band
v7: a-type band v8: c-type (half) band
4 = 1 0
4 = 2 1
4 = 3 2
4 = 4 3
Good visibility of v4 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 = 17573 lines measured in the 110-374 GHz FASSST spectrum
Rotation-vibration transitions in 7 different bands (3 fundamental and 4 hot bands) = 2005 lines measured in the CLS 50-350 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 0.0001 cm-1 measurement uncertainties
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 http://info.ifpan.edu.pl/~kisiel/prospe.htm)
I also recommend PISLIN
Obs.
Calc.
Reproduction of the S(CN)2 v4 b-type band using AABS:P-transition region
indicator of transition present in the data set
Reproduction of the S(CN)2 v7 a-type band:
Obs.
Calc.
Q-transition region
Blanking known lines in the v4 region:
original
blanked
S(CN)2 energies
Infrared dark state (A2 symmetry) only accessible via perturbations in pure rotational transitions in the FASSST spectrum
120.753288(5)
241.785568(5)
363.098148(6)
308.782880(6)
484.692211(7)
606.566678(22)
472.181464(11)
483.434706(12)
490.243684(11)
351.399591(7) 362.527264(8)
From global fit of FASSST+CLS data
120.753288(5)
308.782880(6)
351.399591(7)
362.527264(8)
490.243684(11)
Comparison of fundamental wavenumbers with previous harmonic estimate:
Kisiel et al., J.Mol.Spectrosc. 246, 39 (2007)
120.753288(5)
241.785568(5)
363.098148(6)
484.692211(7)
606.566678(22)
4
4 + 4 + 2 x44
24 + 4 + 4 x44
34 + 4 + 6 x44
44 + 4 + 8 x44
Evaluation of x44 as a double check on vibrational energies:
x44= 0.1395 cm-1
x44= 0.1398 cm-1
x44= 0.1401 cm-1
x44= 0.1402 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 Bv-B0 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 Bv-B0 values with estimates from ab initio anharmonic calculation (made with CFOUR) is encouraging and the re
SE geometry will be evaluated
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:
Special thanks: OSU International Symposium on Molecular Spectroscopy and the local organisers
