1. 1 Fourier transform microwave and infrared study of silacyclobutane Cody van Dijk, Samantha van Nest, Ziqiu Chen and Jennifer van Wijngaarden Department of Chemistry, University of Manitoba, Winnipeg MB R3T 2N2

2. 2 ▪ precursor for SiC film deposition ▪ previous low resolution microwave † and far IR ‡ spectra ▪ double-well potential for puckering mode ▪ no observation of inversion tunnelling in early microwave spectra Silacyclobutane (SCB) † W. C. Pringle, J Chem. Phys. 54, 4979 (1971). ‡ J. Laane and R. C. Lord, J. Chem. Phys. 48, 1508 (1968).

3. 3 Fourier Transform Microwave (FTMW) Spectroscopy Specifications ● Range: 4-26 GHz (8 - 1 cm) ● Line widths ~7 kHz ● Temperature: 1 K

4. 4 Selection rules for the microwave spectrum of SCB ▪ tunneling states (blue and purple) ▪ a-type transitions within a state ▪ c-type transitions connect states ▪ closed loops help! J K a K c a c

5. 5 0 00 – 1 01 ▪ can resolve tunneling splitting of 10 kHz! a-type microwave transition 20 cycles

6. 6 c-type microwave transition 0 00 ( 0 + ) – 1 10 ( 0 – ) 2000 cycles ▪ 0 00 (0 – )→ 1 10 (0 + ) transition found 150 MHz lower

7. 7 MW spectroscopic constants for SCB ▪ 15 lines fit, 11 independent parameters 8815.75 6289.00 4245.32 Previous MW

8. 8 Far infrared spectrum of the ring puckering mode ▪ J. Laane and R. C. Lord, J. Chem. Phys. 48, 1508 (1968) 157.8 cm –1 hotbands

9. 9 Barrier to planarity ▪ A. Al-Saadi and J. Laane, Organometallics. 27, 2435 (2008)

10. 10 Far IR spectroscopy at the Canadian Light Source Aperture 1.3 mm Resolution 0.00096 cm –1 max Beamsplitter Ge-mylar Detector Si bolometer Bruker IFS125HR Pressure 2 – 3 Torr Pathlength 80 m Temperature 250 K or 298 K 2 m multipass cell Conditions for 157 cm –1

11. 11 Ring puckering mode of SCB ▪ 2 Torr pressure, T= 250 K, 80 m pathlength ▪ 6 days of averaging ▪ linewidths ~ 0.0015 cm –1 ▪ expect ~0.3 cm –1 inversion tunneling splitting wavenumber Synchrotron July 2008

12. 12 wavenumber P branch structure

13. 13 Hg Arc lamp April 2009 A second look … ▪ 3 Torr pressure, T= 298 K, 80 m pathlength ▪ 11 days of averaging wavenumber

14. 14 Higher vibrational bands of SCB

15. 15 Far and Mid IR spectra from the CLS July/September 2008 298 K, 40 m pathlength May 2009 298 K, 80 m pathlength 13 mTorr 170 mTorr 35 mTorr wavenumber

16. 16 P branch structure of the ν 14 band wavenumber

17. 17 Wouldn’t it be nice… wavenumber

18. 18 Loomis Wood plot of the ν 14 band wavenumber

19. 19 Assignment of the ν 14 band wavenumber

20. 20 Spectroscopic parameters for the ν 14 band of SCB MW 0.2940595(3) 0.2097793(3) 0.1416076(2) 0.2940599(3) 0.2097796(3) 0.1416059(2) ~1500 lines -the work continues…

21. 21 Acknowledgements ▪ SCB synthesis Prof. John Sorensen (U. Manitoba) ▪ CLS project Dr. Brant Billinghurst (CLS) Accepting new graduate students! Please contact me for details.