1. Tunneling Effects and Conformation Determination of The Polar Forms of 1,3,5 Trisilapentane
Frank E. Marshalla, William Raymond Neal Tonksb , David Joseph Gillcrista, Charles J. Wurreyc, Gamil A. Guirgisb, G. S. Grubbs IIa
aMissouri University of Science and Technology
bCollege of Charleston
CUniversity of Missouri, Kansas City

2. Motivation
Contacted by Gamil Guirgis from the College of Charleston, South Carolina
1,3,5 Trisilapentane had never been studied in the Microwave regime
Interest in conformation orderings
Interest in silyl rotors

3. Energy Difference (cm-1)
Theoretical Data
Theoretical information was provided
Utilizes MP2(Full)/6-311+G(2d,2p) methods
4 Different conformations predicted
C2 should not be detectable due to minimal dipole
Cs has sizable dipole, however the energy barrier is large
Conformation
Dipole X Y Z C2
0.00
0.0625 C1
1.007
0.8197
C2V
4.8834 Cs
0.623
0.8458
Conformation
Energy Difference (cm-1) C2 C1
145
C2v
196 Cs
667

4. C1 conformation
Conformation: C1 X Y
1.007 Z
0.8197

5. C2V Conformation
Conformation:
C2V X
0.00 Y Z
4.8834

6. Missouri S&T CP-FTMW 6-18 GHz linear frequency sweep (“chirp”)
Expandable to 2-18 GHz with a specific amplifier
4us, 6GHz chirps
Low noise, High fidelity instrument
Minimal number of parts
AWG and Oscilloscope eliminate multiple circuit components
23GHz, 100GS/s oscilloscope
40W Solid state power amplifier
50GS/s digitization rate, 20GHz bandwidth AWG
Insert ArHCl spectra.

10. Data Analysis
Initial Fits done via Pickett in tandem with the AABS1 package
C1 fits
Approximately 80 lines
A and E states have been fit
1)Z. Kisiel, PROSPE – Programs for Rotational SPEctroscopy, URL: kisiel/prospe.htm
A states
E states

11. Data Analysis C2V Fits Only 18 Lines
Only some of the E states have currently been identified

12. Silyl Rotor Analysis Fits in XIAM have so far proven unsuccessful
Only C1 has been analyzed thus far
C2V is still ongoing
Letting the structure vary has yielded unreasonable structures
Letting barrier heights vary has yielded unreasonable results
Letting f vary yields unreasonable results
To our knowledge, no program can fit a C1 molecule with 2 tops. Any suggestions on how to attempt this problem would be appreciated!

13. Acknowledgements Dr. Garry Grubbs Dr. Gamil Guirgis Lab Members
University of Missouri Research Board Grant
Pictures of Galen, Brooks, Corey Evans