Synchrotron-based study of the far infrared spectrum of silacyclobutane: the ν29 and ν30 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)

2

0+0-

1+1-

Ring puckering angle θ

440

cm-1

2+2-

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

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-12+

2-E

FTMW spectrum

a-type

Canadian Light Source, CLS

NH

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

Far-infrared experiments at CLS

7

LiAlH4

110 ˚C

Exp. Parameter FIR set up

Spectrometer Bruker IFS 125 HR FTIR

Aperture 1.3 mm

Resolution

(instrumental)

0.000959 cm-1 (360-500

cm-1)

0.001920 cm-1 (100-200

cm-1)

Absorption pathlength 72 m

Cell temperature 298 K

380 400 420

cm-1

440

8

The ν29 SiH2 rocking mode

6 μm Mylar BS/GeCu Detector

528 interferograms, ~53 h

448 mTorr

392.9 391.1 391.3

cm-1

391.4391.2391.0

How can we assign them?

9

Loomis-Wood plot of the ν29 band: c-type progressions

10

11

oeoo

eoee

A2A1

B2B1

oeoo

eoee

A2A1

B2B1

oeoo

eoee

B2B1

A2A1

oeoo

eoee

B2B1

A2A1

Ring inversion (B1)

ν29 SiH

2 rocking mode (B

1)

ν29 SiH

2 rocking mode (B

1)

0-(B1) 0+ (A1)

ν29+ (B1)

c-type transitions

c-type transitionsν29

- (A1)

392.9 391.1 391.3

cm-1

391.4391.2391.0

12

29 27 2 30 28 2

30 26 4 31 27 4

30 25 5 31 26 5

28 28 0 29 29 031 24 7 32 25 8

29 27 2 30 28 2

31 23 8 32 24 829 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 24 829 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- → ν29 -0+ → ν29 +

Loomis-Wood plot of the ν29 band: c-type progressions

13

0- → ν29 -0+ → ν29 +

14

Loomis-Wood plot of the ν29 band: a-type progressions 0- → ν29 +

0+ → ν29 -

15

oeoo

eoee

A2A1

B2B1

oeoo

eoee

A2A1

B2B1

oeoo

eoee

B2B1

A2A1

oeoo

eoee

B2B1

A2A1

Ring inversion (B1)

ν29 SiH

2 rocking mode (B

1)

ν29 SiH

2 rocking mode (B

1)

0-(B1) 0+ (A1)

ν29+ (B1)

c-type transitions

c-type transitions

a-type transitions

a-ty

pe tr

ansit

ions

ν29- (A1)

~ 6500 transitions assigned

16

Loomis-Wood plot of the ν29 band: a- and c-type progressions

cm-1

0.20.10.0-0.1-0.2

0- → ν29 -0+ → ν29 +

0- → ν29 +0+ → ν29 -

17

The Q branch of the ν29 band

cm-1

Exp.

Sim.

18

The ν30 ring puckering mode

130 140 160cm-1

180150 170

75 μm Mylar BSSi bolometer

844 interferograms, ~42 h

1060 mTorr, 0.00192 cm-1

0.0

cm-1

-0.2 -0.1 0.1 0.2

19

Loomis-Wood plot of the ν29 band: c-type progressions 0- → ν30 -

0+ → ν30 +

Spectroscopic parameters for the ν29 and ν30 modes of SCB• Global fit of the ν29 and ν30 modes

• ~8,000 transitions• Ground state constants held fixed to values determined from GSCDs

20

21

0 -0 +

ν29 -

0.00254798(7)

158.38466115(11)

158.1218438(2)

410.20889633(7)

410.03760177(14)

ν29 +

ν30 -

ν30 +

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-1

90 120 180

23

Acknowledgement

Dr. van Wijngaardens group:Cody van DijkSamantha Harder

Dr. Wallace Pringle (Wesleyan University) Dr. Brant Billinghurst (Canadian Light Source)