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Fourier transform microwave and

infrared study of silacyclobutane

Cody van Dijk, Samantha van Nest, Ziqiu Chenand Jennifer van Wijngaarden

Department of Chemistry, University of Manitoba, Winnipeg MB R3T 2N2

SiH

H

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)Silacyclobutane (SCB)

SiH

H

†W. C. Pringle, J Chem. Phys. 54, 4979 (1971).‡J. Laane and R. C. Lord, J. Chem. Phys. 48, 1508 (1968).

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Fourier Transform Microwave (FTMW) Fourier Transform Microwave (FTMW) SpectroscopySpectroscopy

Specifications● Range: 4-26 GHz (8 - 1 cm)● Line widths ~7 kHz● Temperature: 1 K

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Selection rules for the microwave spectrum of Selection rules for the microwave spectrum of SCBSCB

▪ tunneling states (blue and purple)

▪ a-type transitions within a state

▪ c-type transitions connect states

▪ closed loops help!

J Ka Kc

a

c

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000 – 101

▪ can resolve tunneling splitting of 10 kHz!

a-typea-type microwave transition microwave transition

20 cycles

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c-typec-type microwave transition microwave transition

000(0+) – 110(0–)

2000 cycles

▪ 000(0–)→ 110(0+) transition found 150 MHz lower

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MW spectroscopic constants for SCBMW spectroscopic constants for SCB

ν 0 75.7138(40) Rotational constants /MHz

A 8815.6812(75) 8815.6933(75) B 6289.0254(81) 6289.0351(83) C 4245.2389(63) 4245.2376(62)

Centrifugal distortion constants /kHz ΔJ 2.86(31) 2.86† ΔJK –5.05(54) –5.05 ΔK 8.01(42) 8.01 δK 0.0130(16) 0.0130

rms error /MHz 0.0054 †fixed to ground state values

▪ 15 lines fit, 11 independent parameters

8815.756289.004245.32

Previous MW

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Far infrared spectrum of the ring puckering Far infrared spectrum of the ring puckering modemode

▪ J. Laane and R. C. Lord, J. Chem. Phys. 48, 1508 (1968)

157.8 cm–1

hotbands

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Barrier to planarityBarrier to planarity

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

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Far IR spectroscopy at the Canadian Light SourceFar 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 K2 m multipass cell

Conditions for 157 cm–1

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Ring puckering mode of SCBRing 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

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wavenumber

P branch structureP branch structure

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Hg Arc lamp April 2009

A second look …A second look …

▪ 3 Torr pressure, T= 298 K, 80 m pathlength▪ 11 days of averaging

wavenumber

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Higher vibrational bands of Higher vibrational bands of SCBSCB

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Far and Mid IR spectra from the CLSFar and Mid IR spectra from the CLS

July/September 2008298 K, 40 m pathlength

May 2009298 K, 80 m pathlength

13 mTorr170 mTorr

35 mTorr

wavenumber

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P branch structure of the P branch structure of the νν1414 bandband

wavenumber

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Wouldn’t it be nice…Wouldn’t it be nice…

wavenumber

NH

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Loomis Wood plot of the Loomis Wood plot of the νν1414 bandband

wavenumber

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Assignment of the Assignment of the νν1414 band band

wavenumber

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Spectroscopic parameters for the Spectroscopic parameters for the νν1414 band of SCB band of SCB

MW0.2940595(3)0.2097793(3)0.1416076(2)

0.2940599(3)0.2097796(3)0.1416059(2)

ν 0 737.27552(2) 0 737.28731(2)

A 0.294182(4) 0.293960(4) 0.29447(1) 0.29423(1) B 0.209720(2) 0.209464(2) 0.209566(3) 0.209319(3) C 0.1416084(3) 0.1414625(3) 0.1416097(4) 0.1414651(4) ΔJ 0.121(1) 0.102(1) 0.133(5) 0.109(5)

ΔJK –1.82(3) –1.33(3) –1.8(1) –1.1(2) ΔK 3.91(2) 2.99(2) 3.7(2) 2.4(2) δJ 0.0414 0.0316 0.047(2) 0.035(2) δK –0.684 –0.493 –0.62(4) –0.36(4)

rms error /cm–1 0.000131 0.000150

~1500 lines ~1500 lines

-the work continues…

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AcknowledgementsAcknowledgements

▪ SCB synthesisProf. John Sorensen (U.

Manitoba)

▪ CLS projectDr. Brant Billinghurst (CLS)

Accepting new graduate students! Please contact me for details.