OSU International Symposium on Molecular Spectroscopy June 18 – 22, TF Infrared/Raman -- TF01, Tuesday, June 19, 2012

National Synchrotron Research Facility

At the core of the Canadian Light Source is a series of two particle accelerators: an electron Linac and booster synchrotron. The third accelerator is an electron storage ring which operates at a current of 250 mA and an energy of 2.9 GeV The long stored beam lifetime has permitted electron reinjection to be reduced to twice per day. The storage ring supports 14 independent beam lines from the THz region (about eV) to hard X-rays (more than 100 keV)

Inside the hutch of the CLS far-infrared beamline, showing the Bruker IFS 125-HR Fourier transform spectrometer. Wavenumber range: 10 – 1000 cm -1, Frequency range: 0.3 – 30 THz, Energy range: 1.3 – 125 meV Beamline transfer optics inside vacuum chambers 2m White cell Bruker IFS 125-HR spectrometer: Optical path difference 9.4 m or instrumental line widths as narrow as cm -1 or 19 MHz before apodization

My first chemical synthesis of SCl 2, a substance that cannot be shipped anymore in the US or Canada since May All chemical syntheses were carried out at the CLS. ClSSCl + Cl 2 2SCl 2 Lecture bottle Cl 2

AgCN + SCl 2 = 2AgCl + S(CN) 2 S(CN) 2 + thermal isomerization = NCNCS Z. Kisiel et al. Journal of Molecular Spectroscopy 246 (2007) bb cm cm cm cm -1 CLS work High resolution FT-IR measurements available

Ab initio equilibrium structure of NCNCS CCSD(T)/cc-pV5Z level of theory Winnewisser et al. Large amplitude bending potential function μbμb μaμa MP2 Intensities _km/mol_

a-type transitions: ΔJ = 0, ± 1 and ΔK a = 0 b-type transitions: ΔJ = 0, ± 1 and ΔK a = ± 1 Δv b = 0, 1, 2, 3, … ΔK a = +1 Sub-bands ΔK a = -1 Sub-bands

GSRB predicted FIR Spectrum limited to J ≤ 10, v b ≤ 6. Overlaid S/N enhancement for measurement through 150 m cm -1 resolution: Synchrotron versus laboratory FIR source. A. R. W. McKellar, J. Mol. Spectroscopy 262 (2010) 1 – 10. Pyrolytic isomerization reaction of sulfur dicyanide, S(CN) 2 yields cyanogen iso-thiocyanate, NCNCS + other species

a-type FIR sum stick-spectrum Predicted for NCNCS

b-type FIR sum stick-spectrum predicted for NCNCS

S(CN) 2 predictions: 1 CN symmetric stretch 2262 cm -1 and 5 CN asymmetric stretch 2247 cm -1 According to ab initio calculations our target molecule NCNCS should exhibit two strong absorptions: 1 = 2258 cm -1 and 2 =2024 cm -1 NCNCS 1) For this spectrum the vapor of S(CN) 2 was drawn through the pyrolysis zone at a temperature of 855 o C and trapped under liquid N 2 und released into the 2m White absorption cell at a trap temperature of -40 o C 2) This 2262 cm -1 band was also obtained before attempting the pyrolysis of S(CN) 2 which indicated to us last year that the carrier of this absorption should be S(CN) 2. The answer to the S(CN) 2 / NCNCS puzzle is: NCNCS is the more stable isomer and S(CN) 2 converts already at room temperature in the cell!

Sample of dense but very assignable spectra of both S(CN) 2 and NCNCS S(CN) 2, 4, R-branch FWHH = cm -1

Identification of NCNCS rotation-vibration spectra at the Canadian Light Source – May 28, 2012 The two IR bands shown in the previous slide were recorded in June 2011 at the CLS. The bands could be obtained from either S(CN) 2 directly admitted into the 2m cell (set for 72 m path length) or from vapor trapped in liquid nitrogen after pyrolysis of S(CN) 2. For the most prominent series in the NCNCS band at 2024 cm -1, the lower-state combination differences (CDs) of the form (J+1) 0(J+1) – (J-1) 0(J-1) and thus the B eff values are consistent with those for the ground state, K a = 0 levels calculated from MMW data of NCNCS [PCCP 12, , 2010] to within cm -1 for (so far) J = 10 to 80. /cm -1 MMW /cm -1 Infrared

NCNCS spectra observed in high resolution at the CLS in May and June 2012 Predicted bands: 5 = 472 cm -1  = 454 cm -1 6 = 447 cm -1  = 429 cm -1 Unassigned overtone or difference bands   1178 cm = 662 cm -1 H2OH2O

Conclusions from our measurement campaigns at the Canadian Light Source in May/June of 2011 and )The Doppler limited high resolution spectra of S(CN) 2 and NCNCS can be measured. 2)In order to obtain quality spectra for NCNCS the chemical handling must be improved. 3)Vapor pressure measurements for NCNCS should be carried out. 4)The detection of the weak quasi-linear bending mode of NCNCS should be possible.