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

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

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

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 MW spectroscopic constants for SCB ▪ 15 lines fit, 11 independent parameters Previous MW

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

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

10 Far IR spectroscopy at the Canadian Light Source Aperture 1.3 mm Resolution 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 Ring puckering mode of SCB ▪ 2 Torr pressure, T= 250 K, 80 m pathlength ▪ 6 days of averaging ▪ linewidths ~ cm –1 ▪ expect ~0.3 cm –1 inversion tunneling splitting wavenumber Synchrotron July 2008

12 wavenumber P branch structure

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

14 Higher vibrational bands of SCB

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

16 P branch structure of the ν 14 band wavenumber

17 Wouldn’t it be nice… wavenumber

18 Loomis Wood plot of the ν 14 band wavenumber

19 Assignment of the ν 14 band wavenumber

20 Spectroscopic parameters for the ν 14 band of SCB MW (3) (3) (2) (3) (3) (2) ~1500 lines -the work continues…

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