1. Room-Temperature Chirped-Pulse Microwave Spectrum of 2-Methylfuran
Ian A. Finneran
Steven T. Shipman
New College of Florida

2. Senior Thesis Project
Room-temperature microwave spectroscopy of small molecules with methyl rotors
2-Methylfuran
ortho-Fluorotoluene
Anisole

3. Room Temperature Microwave Spectroscopy
Excited vibrational states
Vibrational-rotational coupling constants (α’s)
High J,K transitions

4. The New College Spectrometer1)
Generate pulse
Amplify pulse
Send pulse to waveguide
Amplify molecular emission
Record, average emission
in the time domain
6) Fourier transform to get spectrum 2) 3) 4)
5), 6)

5. XIAM Internal-Axis Method (hybrid of RAM and PAM)
Recompiled up to J=99
Used AABS for GUI with several Python scripts
Fit rigid rotor parameters (including distortion) and four internal rotational parameters:
V3 = barrier to internal rotation
Iα = Moment of inertia of methyl group
θ, φ = angles of methyl group with respect to PAS
H. Hartwig and H. Dreizler, Z. Naturforsch 51a, (1996).
I. Kleiner, J. Mol. Spec. 260, 1-18 (2010).
Z. Kisiel, L. Pszczolkowski, I.R.Medvedev, M. Winnewisser, F. C. De Lucia, C. E. Herbst, J. Mol. Spec. 233, (2005).

6. 2-Methylfuran Small, planar molecule Calc. Qvib = 4.5 at 298 K
Moderate dipole moment
μ = 0.65 ± 0.03 D
μa = 0.31 ± 0.04 D
μb = 0.57 ± 0.02 D
Calc. barrier = 370 cm-1
B3LYP/6-311+G(d,p)
Exp. Barrier = 411 cm-1

7. Previous MW Work on 2-Methylfuran
Norris and Krisher (1969)
12-33 GHz Stark-modulated spectrometer
No peaks in X-band (8-12 GHz)
74 Ground state a- and b-types fit
Andresen and Dreizler (1970)
GHz Stark-modulated spectrometer
Dipole fit with 6 peaks (3 A-E pairs)
μ = 0.65 ± 0.03 D
μa = 0.31 ± 0.04 D
μb = 0.57 ± 0.02 D
W. G. Norris and L. C. Krisher, J. Chem. Phys. 51, (1969).
U. Andresen, and H. Dreizler, Z. Naturforschung 25a, 570 (1970).

8. Internal Rotation E Rigid Molecule A Or High Barrier Medium Barrier E
Intensity
Intensity
Frequency
Frequency

9. Internal Rotation E Rigid Molecule A Or High Barrier Low Barrier E A
Splitting is
related
to barrier height
Intensity
Intensity
Frequency
Frequency

10. Forbidden c-types
Occur when K-splitting is close in magnitude to A-E splitting
K-splitting dependent on:
Symmetry of Molecule, κ (Ray’s asymmetry parameter)
K quantum number
A-E splitting dependent on barrier height

11. Example: R-Branch, vt=1 κ ~ -0.67 for 2-methylfuran
Adapted from Gordy and Cook,
fig and 12.8

12. E-state transitions for 2-mf ground state (XIAM, 298 K)

13. 2-methylfuran
3 million averages
Noise ~ 0.3 units
273 K, 11 mTorr
2 ms FID

16. Prediction includes b-types with ΔKa=±1, ΔKc=±1
Relationship to A-state rigid rotor quantum numbers:
L: shares lower state r. r. quantum numbers
U: shares upper state r. r. quantum numbers
Prediction includes b-types with ΔKa=±1, ΔKc=±1

17. 1.2 MHz FWHM is due primarily to 2 ms FID collection time.

19. Ground State and Tentative Excited StateGS
Current
Previous (Norris and Krisher)
vt=1
158 cm-1
(Tentative)
Ab initio (α’s) B3LYP/
6-311+G(d,p)
A (MHz)
(7)
(2)
B (MHz)
(3)
(1)
C (MHz)
(8)
(3)
ΔJ (kHz)
1.33(8) –
5.6(3)
ΔJK (kHz)
-2.13(8)
-2.13 (fixed)
ΔK (kHz)
0.83(3)
-3.0(6)
δJ (kHz)
0.49(3)
2.2(1)
δK (kHz)
-0.475(5)
0.8(2)
V3 (cm-1)
411.0(2)
416.2(244)
401.4(1)
Jmax A,E
78,71
15,15
15,7
θ (degrees)
5.3(1)
 3.4
8.7(1)
φ (degrees)
90.0 (fixed)
90.0
98.2(1)
Iα (uA2)
3.175(1)
3.14 (fixed)
3.224(1) N
278 (A=115, E=163)
74, A=37, E=37
33 (A=25, E=8)
RMS (kHz)
118
1193 98

20. Conclusions/Future Work for 2-Methylfuran
Observed forbidden c-types in ground state
Tentative fit of first torsionally excited state
Obtained more accurate value for V3
Still many unassigned peaks
311 assigned / 3091 total ~ 11%
Need data from GHz to assign higher J and excited vibrational states

21. Acknowledgments Katherine Raoux Dale Musselman Kaitlin Lovering
New College of Florida
Research Corporation
ACS Petroleum Research Fund
National Science Foundation
Katherine Raoux
Dale Musselman
Kaitlin Lovering
Sophie Lang
Erin Kent
Morgan McCabe
Maria Phillips
Bri Gordon

23. Internal Rotation

24. Final Results 2-Methylfuran ortho-Fluorotoluene Anisole
311 peaks assigned (10%)
Barrier = 411 cm-1
ortho-Fluorotoluene
398 peaks assigned (11%)
Barrier = 238 cm-1
Anisole
649 peaks assigned (26%)
Barrier > 1100 cm-1
Aromaticity and sterics?

25. κ ~ for 2-methylfuran

26. Data taken at 298 K, so high K’s are common!

27. Peaks assigned in the X-band!