1. Bri Gordon Steven T. Shipman New College of Florida
Waveguide Chirped-Pulse Fourier Transform Microwave Spectra of 2-Propanethiol
Bri Gordon
Steven T. Shipman
New College of Florida

2. Astrochemistry of Alkylthiols
Few organosulfur compounds have been observed in the ISM.
Methanethiol has been observed in Sagittarius B2.*
*Linke, R.A.; Frerking, M. A.; Thaddeus, P.; Astrophysical Journal 234, L139 (1979).
Larger alkylthiols may be present; existing fits should be extended in order to search for them in the ISM.

3. Chirped-Pulse Spectrometer1
Generate pulse
Amplify pulse
Send pulse to waveguide
Amplify molecular emission
Record, average emission in the time domain
Fourier transform the emission
Chirped Pulse
(Linear Frequency Sweep) 1) 2) 3) 4)
5), 6)

4. Senior Thesis Research1
Worked with three previously studied small alkylthiols.
High vapor pressures and strong dipoles:
Ethanethiol
1-propanethiol
2-propanethiol
g-EtSH
0 cm-1
g'-EtSH
0 cm-1
t-EtSH
213.3 cm-1 1
TG-1-PrSH
0 cm-1
TG’-1-PrSH
0 cm-1
TT-1-PrSH
249.5 cm-1 1
t-2-PrSH
0 cm-1
g-2-PrSH
41.3 cm-1
g’-2-PrSH
41.3 cm-1
DFT B3LYP / G(d,p)

5. Tunneling interactions in EtSH1
Thiol Potential Energy Scan in EtSH 1
trans
gauche'
gauche
trans
The thiol H-atom tunneling through the potential barrier
The tunneling induces symmetric and antisymmetric states.
c - type transitions between these states are split by as much as 3.5 GHz.
Previous*
Ab Initio** V2
-135 (27)
(18) V3
456.4 (20)
(17)
*Nakagawa, J., Kuwada, K., Hayashi, M. Bull. Chem. Soc.
Jpn. 49, 3420 (1976).
**DFT B3LYP/ G(d,p)

6. Tunneling interactions in 2-PrSH1 1
Thiol Potential Energy Scan in 2-PrSH
trans
gauche'
gauche
trans
b - type transitions between states show tunneling splitting
Previous*
Ab Initio** V2 -
47.74 (14.4) V3
657.54
(13.4)
*Griffiths, J. H. J. Mol.Spec., 56, 257 (1975).
**DFT B3LYP/ G(d,p)

7. 964 peaks above the 3:1 signal to noise threshold
2-Propanethiol 1
(D)
trans* µa
1.75 µb
0.004 µc
0.38
µtot
1.80
2 million averages, 7 mTorr, -20° C, 4 μs Fid
Experimental
Simulated trans
Simulated gauche
(D)
gauche* µa
1.52 µb
0.70 µc
µtot
1.81
*DFT B3LYP / G(d,p)
964 peaks above the 3:1 signal to noise threshold

8. 964 peaks above the 3:1 signal to noise threshold
2-Propanethiol 1
(D)
trans* µa
1.75 µb
0.004 µc
0.38
µtot
1.80
2 million averages, 7 mTorr, -20° C, 4 μs Fid
Experimental
Simulated trans
Simulated gauche
(D)
gauche* µa
1.52 µb
0.70 µc
µtot
1.81
*DFT B3LYP / G(d,p)
964 peaks above the 3:1 signal to noise threshold

9. 2-Propanethiol: trans Conformer Expanded View1
- Experimental
- Simulated trans
Previous*
Current
Lines Fit 12
126
Fit RMS (kHz) 50 69
Max J 4 80
# of Lines
a – type 78
b – type -
c – type 48
*Griffiths, J. H.; J. Mol.Spec., 56, 257 (1975).

10. 2-Propanethiol: gauche Conformer Expanded View1
Experimental
Simulated gauche
Previous*
Current
Lines Fit 55
265
Fit RMS (kHz) 50
112
Max J 5 42
# of Lines
Max Splitting (MHz)
a – type 96
107.6
b – type 73
1124.6
c – type
91.7
*Griffiths, J. H. ; J. Mol.Spec., 56, 257 (1975).

11. g-2-PrSH Splitting Transition Frequency (MHz) Splitting (MHz) 7 4 3 ←
7 3 4
(+ -)
(- +)

12. Results g-2-PrSH Hamiltonian: Ĥ = Ĥ+++ Ĥ-- + Ĥ+-
Ĥ++ = A+ Ĵa2 + B+Ĵb2 + C+Ĵc2
Ĥ-- = A–Ĵa2 + B–Ĵb2 + C–Ĵc2 + ∆ν
Ĥ+- = Fa (ĴbĴc + ĴcĴb) + Gc (iĴc) + Fc (ĴaĴb + ĴbĴa)
gauche
trans
Ab Initio*
Current
A (MHz) 
(12)
(8)
B (MHz) 
(11)
(7)
C (MHz) 
(8)
(7)
∆v (MHz)  -
(21)
Fa (MHz)
(29)
Gc (MHz)
8.19 (22)
Fc (MHz)
(132)
DJ (kHz)
1.5
1.454 (35)
1.3
1.3 (fixed)
DJK (kHz)
2.4
2.344 (62)
2.7
2.61 (12)
DK (kHz)
2.6
2.97 (16)
2.77 (33)
dJ (kHz)
0.44
0.453 (4)
0.37
0.366 (7)
dK (kHz)
3.3
3.390 (47)
2.8
2.997 (92)
ФKJ (HZ)
(7)
Lines Fit
265
126
RMS (kHz)
112 69
Max J 42 80
* DFT B3LYP/ G(d,p)

13. Conclusions and Future Work
391 (41%) of the 964 peaks have been assigned to the trans and gauche ground state normal species.
Next spectra to fit are vibrationally excited states and 34S species

14. Acknowledgments 1 Professor Shipman
Ben Rooks
Maria Phillips
Christian Metzger
Ian Finneran
Ben Reinhold
New College of Florida
The National Science Foundation
This material is based upon work supported by the National Science Foundation Division of Chemistry under Grant No  (co-funded by MPS/CHE and the Division of Astronomical Sciences).

15. The Galactic Centre and Sagittarius B2, from the European Southern Observatory

16. The Galactic Centre and Sagittarius B2, from the European Southern Observatory

17. Laboratory improvements: 18-26.5 GHz Spectrometer
Our previous frequency range was GHz
A new circuit was built to extend it to GHz (left).

18. 2-Propanethiol 1 2 million averages, 7 mTorr, -20° C, 4 μs Fid
964 peaks above the 3:1 signal to noise threshold