1. Synchrotron-based study of the far infrared spectrum of silacyclobutane: the ν 29 and ν 30 bands Ziqiu Chen, Cody W. van Dijk, Samantha Harder and Jennifer van Wijngaarden Department of Chemistry, University of Manitoba, Winnipeg, Canada

2. Ring puckering potential of silacyclobutane (SCB) 2 0+ 0- 1+ 1- Ring puckering angle θ 440 cm -1 2+ 2- E Si C C C a b β

3. Previous low resolution work 3 W.C. Pringle, J. Chem. Phys. 54,4979 (1971) MW J. Laane and R. C. Lord, J. Chem. Phys. 48, 1508 (1968) A.A. Al-Saadi and J. Laane, Organometallics, 27, 3435 (2008) IR

4. 4 Previous high resolution MW work 0- 0+ J. van Wijngaarden, Z. Chen, C.W. van Dijk and J.L. Sorensen, J. Phys. Chem. A 115, 8650 (2011) 0+ 0- 1+ 1- Ring puckering angle θ 440 cm -1 2+ 2- E FTMW spectrum a-type

5. Canadian Light Source, CLS

6. D. W. Tokaryk and J. van Wijngaarden, Can J. Phys. 87, 443-448 (2009).

7. Far-infrared experiments at CLS 7 LiAlH 4 110 ˚C Exp. ParameterFIR set up SpectrometerBruker IFS 125 HR FTIR Aperture1.3 mm Resolution (instrumental) 0.000959 cm -1 (360-500 cm -1 ) 0.001920 cm -1 (100-200 cm -1 ) Absorption pathlength72 m Cell temperature298 K

8. 380400420 cm -1 440 8 The ν 29 SiH 2 rocking mode 6 μm Mylar BS/GeCu Detector 528 interferograms, ~53 h 448 mTorr

9. 392.9 391.1 391.3 cm -1 391.4 391.2 391.0 How can we assign them? 9

10. Loomis-Wood plot of the ν 29 band: c-type progressions 10

11. 11 oe oo eo ee A2A2 A1A1 B2B2 B1B1 oe oo eo ee A2A2 A1A1 B2B2 B1B1 oe oo eo ee B2B2 B1B1 A2A2 A1A1 oe oo eo ee B2B2 B1B1 A2A2 A1A1 Ring inversion (B 1 ) ν 29 SiH 2 rocking mode (B 1 ) 0 - (B 1 ) 0 + (A 1 ) ν 29 + (B 1 ) c -type transitions ν 29 - (A 1 )

12. 392.9 391.1 391.3 cm -1 391.4 391.2 391.0 12 29 27 2 30 28 2 30 26 4 31 27 4 30 25 5 31 26 5 28 28 0 29 29 0 31 24 7 32 25 8 29 27 2 30 28 2 31 23 8 32 24 8 29 26 3 30 27 3 30 25 5 31 26 5 28 28 0 29 29 0 30 24 6 31 25 6 28 27 1 29 28 1 31 23 8 32 24 8 29 26 3 30 27 3 29 25 4 30 26 4 30 24 6 31 25 6 28 27 1 29 28 1 30 23 7 31 24 7 0- → ν 29 - 0+ → ν 29 +

13. Loomis-Wood plot of the ν 29 band: c-type progressions 13 0- → ν 29 - 0+ → ν 29 +

14. 14 Loomis-Wood plot of the ν 29 band: a-type progressions 0- → ν 29 + 0+ → ν 29 -

15. 15 oe oo eo ee A2A2 A1A1 B2B2 B1B1 oe oo eo ee A2A2 A1A1 B2B2 B1B1 oe oo eo ee B2B2 B1B1 A2A2 A1A1 oe oo eo ee B2B2 B1B1 A2A2 A1A1 Ring inversion (B 1 ) ν 29 SiH 2 rocking mode (B 1 ) 0 - (B 1 ) 0 + (A 1 ) ν 29 + (B 1 ) c -type transitions a -type transitions ν 29 - (A 1 ) ~ 6500 transitions assigned

16. 16 Loomis-Wood plot of the ν 29 band: a- and c- type progressions cm -1 0.20.10.0-0.1-0.2 0- → ν 29 - 0+ → ν 29 + 0- → ν 29 + 0+ → ν 29 -

17. 17 The Q branch of the ν 29 band cm -1 Exp. Sim.

18. 18 The ν 30 ring puckering mode 130140 160 cm -1 180 150170 75 μm Mylar BS Si bolometer 844 interferograms, ~42 h 1060 mTorr, 0.00192 cm -1

19. 0.0 cm -1 -0.2-0.1 0.10.2 19 Loomis-Wood plot of the ν 29 band: c-type progressions 0- → ν 30 - 0+ → ν 30 +

20. Spectroscopic parameters for the ν 29 and ν 30 modes of SCB Global fit of the ν 29 and ν 30 modes ~8,000 transitions Ground state constants held fixed to values determined from GSCDs 20

21. 21 0 - 0 + ν 29 - 0.00254798(7) 158.38466115(11) 158.1218438(2) 410.20889633(7) 410.03760177(14) ν 29 + ν 30 - ν 30 + Energy differences in cm -1 and not to scale

22. 22 Future work : ring puckering manifold W.C. Pringle, J. Chem. Phys. 54,4979 (1971) cm -1 90120180

23. Acknowledgement Dr. van Wijngaardens group: Cody van Dijk Samantha Harder Dr. Wallace Pringle (Wesleyan University) Dr. Brant Billinghurst (Canadian Light Source) 23