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

Ring puckering potential of silacyclobutane (SCB) Ring puckering angle θ 440 cm E Si C C C a b β

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

Canadian Light Source, CLS

D. W. Tokaryk and J. van Wijngaarden, Can J. Phys. 87, (2009).

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

cm The ν 29 SiH 2 rocking mode 6 μm Mylar BS/GeCu Detector 528 interferograms, ~53 h 448 mTorr

cm How can we assign them? 9

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

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 )

cm → ν → ν 29 +

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

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

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 Loomis-Wood plot of the ν 29 band: a- and c- type progressions cm → ν → ν → ν → ν 29 -

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

18 The ν 30 ring puckering mode cm μm Mylar BS Si bolometer 844 interferograms, ~42 h 1060 mTorr, cm -1

0.0 cm Loomis-Wood plot of the ν 29 band: c-type progressions 0- → ν → ν 30 +

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

ν (7) (11) (2) (7) (14) ν 29 + ν 30 - ν 30 + Energy differences in cm -1 and not to scale

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

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