The far infrared spectrum of thiophosgene Analysis of the 2 and 4 fundamental bands at 500 cm-1 A.R.W. McKellar National Research Council of Canada, Ottawa B.E. Billinghurst Canadian Light Source, University of Saskatchewan, Saskatoon

Cl S Cl Thiophosgene is a formaldehyde analog Planar, C2v symmetry Near-oblate ‘accidental’ symmetric top A ~ 3557 MHz B ~ 3464 MHz C ~ 1753 MHz The axes ‘switch’ with isotopic substitution: For 35Cl2CS, the S-C symmetry axis is the a-inertial axis For 37Cl2CS, the S-C symmetry axis is the b-inertial axis S Cl

Thiophosgene is very popular for studying IVR, intersystem crossing, etc. It’s one of the best-characterized of all molecules in terms of vibrational level structure. But there are no previous systematic high-resolution IR studies.

Why no previous IR studies? Congested spectra! 35Cl35Cl12C32S v = 0 0.337 35Cl37Cl12C32S 0.220 v3 = 1 0.074 v6 = 1 0.068 0.048 0.044 37Cl37Cl12C32S 0.036 v4 = 1 0.030 v2 = 1 0.026 0.020 0.017 35Cl35Cl12C34S 0.015 35Cl37Cl12C34S 0.010 0.008 0.007 Etcetera!!! Relatively heavy molecule Isotopic dilution Hot band dilution The ground state of the principal isotope has only about one third of the total population at room temperature!

3 6 4 2 5 1 Microwave study C-Cl bend 295 cm-1 6 C-Cl rock 312(?) 4 out of plane bend 471 2 C-Cl sym stretch 504 5 C-Cl asym stretch 813 1 C-S stretch 1135 Microwave study Carpenter, Rimmer, Smith, & Whiffen J. Chem. Soc. Faraday Trans. 2 71, 1752-1762 (1975) First complete vibrational assignment Frenzel, Blick, Bennett, & Niedenzu J. Chem. Phys. 53, 199-204 (1969)

2001 survey spectrum from NRC: Bomem DA8 spectrometer, resolution 0 2001 survey spectrum from NRC: Bomem DA8 spectrometer, resolution 0.002 cm-1

CLS Parameters Energy: 2.9 GeV Current: 200 mA Circumference: 171 m 12 straight sections, 5.2 m long RF: 500 MHz, 2.4 MV, supercon Injection: 250 MeV LINAC full energy booster ring Main building: ~ 85 x 85 m

Nominal resolution = 0. 00096 cm-1 Unapodized instrumental width = 0 Nominal resolution = 0.00096 cm-1 Unapodized instrumental width = 0.00064 cm-1 Cl2CS Doppler width = 0.00058 cm-1 Pressure = 0.023 Torr Path = 40 m

resolution matters!

2 band 35Cl35ClCS: lines assigned ~3500; rms error ~0.000065 cm-1 (2 MHz) 35Cl37ClCS: lines assigned ~1330; rms error ~0.000079 cm-1 0 = 503.807 cm-1 A' - A" = -8.3 MHz B' - B" = -2.3 MHz [for 35Cl35ClCS] C' - C" = -3.0 MHz 4 band a few hundred lines assigned 0 = 471.044 cm-1 A' - A" = -2.7 MHz B' - B" = +0.6 MHz [for 35Cl35ClCS] C' - C" = +1.9 MHz

Thiophosgene -- Future Work Extend & complete analysis of the 4 band Coriolis interaction between 2 and 4 ? Can hot bands or 37-37 isotope be assigned ?? Study 3 band ~292 cm-1 Study 6 band ~312 cm-1 (?!?)