Waveguide ChirpedPulse Fourier Transform Microwave CPFTMW Spectrum of

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Waveguide Chirped-Pulse Fourier Transform Microwave (CP-FTMW) Spectrum of ortho-fluorotoluene Ian A. Finneran and Steven

Waveguide Chirped-Pulse Fourier Transform Microwave (CP-FTMW) Spectrum of ortho-fluorotoluene Ian A. Finneran and Steven T. Shipman Division of Natural Sciences New College of Florida 5800 Bay Shore Road Sarasota, FL 34243

Instrument Schematic 1) 250 ns sweep (0. 1 – 4. 9 GHz) generated by

Instrument Schematic 1) 250 ns sweep (0. 1 – 4. 9 GHz) generated by AWG and mixed with PLDRO. 2) Mixed sweep is amplified and sent into sample cell. 3) Molecular FID is amplified, downconverted, and detected with oscilloscope. MW-MW DR measurements can also be made with this setup.

Ortho-fluorotoluene • m. A ≈ m. B ≈ 1 D • Methyl rotor, with

Ortho-fluorotoluene • m. A ≈ m. B ≈ 1 D • Methyl rotor, with V 3 ~ 230 cm-1 • 4 vibrational modes below 400 cm-1 Susskind: Stark-modulated waveguide spectrometer, 12 -38 GHz GS: A (19 transitions), E (15) Two excited states: A 2 (19), A 3 (16) Jacobsen et al. : Molecular beam (4 – 20 GHz) GS: A & E (44 each) Transitions from all 7 13 C isotopomers [1] Susskind, J. Chem. Phys. , 53, 2492 (1970). [2] Jacobsen, S. , Andresen, U. , Mäder, H. , Struct. Chem. , 14, 217 (2003).

o. FT from 8. 7 – 18. 3 GHz o-fluorotoluene 9 m. Torr, 0

o. FT from 8. 7 – 18. 3 GHz o-fluorotoluene 9 m. Torr, 0 °C 2 x 106 averages 4 ms FIDs Noise level at 0. 75 units. Tallest peak has S: N of 98: 1. 8 hours per band (including blank). Line density of ~1 peak per 3 MHz. Threshold Number 25: 1 97 10: 1 648 5: 1 1756 3: 1 3163

Data and Fits Fitting done with XIAM, assignments were made in AABS. Python scripts

Data and Fits Fitting done with XIAM, assignments were made in AABS. Python scripts used to convert. lin files to XIAM format.

Data and Fits We have assigned 12% of the peaks above 3: 1, and

Data and Fits We have assigned 12% of the peaks above 3: 1, and 67 of the 100 most intense transitions.

Ground State Fit Summary Structural Parameters Current Previous [2] A (MHz) 3243. 149(3) 3243.

Ground State Fit Summary Structural Parameters Current Previous [2] A (MHz) 3243. 149(3) 3243. 078(2) B (MHz) 2180. 435(3) 2180. 450(1) C (MHz) 1314. 387(4) ΔJ (k. Hz) Rotor and Fit Quality Parameters Current Previous [2] V 3 (cm-1) 238. 32(19) 227. 28(2)* 1314. 363(1) q (degrees) 30. 788(10) 31. 62(3)* 0. 34(5) 0. 09(1) f (degrees) 90. 01(5) 90. 0 (fixed) ΔJK (k. Hz) -0. 84(5) 0. 01(5) Ia (amu Å2) ΔK (k. Hz) 0. 67(5) 0. 61(11) Jmax A, E δJ (k. Hz) 0. 113(6) 0. 032(7) Nlines δK (k. Hz) -0. 31(3) 0. 06(4) ΦKJ (Hz) -0. 65(5) – ΦK (Hz) 1. 49(11) – sfit (k. Hz) 3. 0938(25) 3. 237 (fixed)* 72, 42 8, 8 334† (A = 178, E = 156) 88 (44 each) 98 143 * When Ia is allowed to vary, V 3 is 237. 0(14), Ia is 3. 11(2), q is 31. 0(2). † Includes assignments from [2] Jacobsen, S. , Andresen, U. , Mäder, H. , Struct. Chem. , 14, 217 (2003).

Excited State Fit Summary (ntors = 1) Structural Parameters Rotor and Fit Quality Parameters

Excited State Fit Summary (ntors = 1) Structural Parameters Rotor and Fit Quality Parameters Current Previous [1] A (MHz) 3226. 725(8) 3217. 74 B (MHz) 2182. 975(6) 2175. 81 V 3 (cm-1) 239. 97(4) – C (MHz) 1313. 438(9) 1314. 445 Q (degrees) 30. 7939(8) – ΔJ (k. Hz) 0. 31(11) – F (degrees) 90. 014(4) – ΔJK (k. Hz) -0. 58(6) – Ia (amu Å2) 3. 0970(5) – ΔK (k. Hz) 0. 40(6) – Jmax A, E 29, 15 6, 0 δJ (k. Hz) 0. 059(8) – Nlines 19 (A only) δK (k. Hz) -0. 52(4) – 116 (A = 106, E = 10) sfit (k. Hz) 72 110 Current Previous [1] A state is definite, E is still tentative. So, uncertainties on rotor parameters are not trustworthy. [1] Susskind, J. Chem. Phys. , 53, 2492 (1970).

Double Resonance Methods for Assignment 505 404 303 202 Double resonance methods reveal level

Double Resonance Methods for Assignment 505 404 303 202 Double resonance methods reveal level connectivity, speeding assignments and removing ambiguity in crowded spectra. 515 414 However - most peaks in spectrum are unconnected to other peaks. 413 For unknown spectra, many possible DR measurements are therefore a waste of time (no connections to reveal). Try pumping multiple features at once to speed the process! 313 212 • • • DR with 10 MHz FWHM pulses Extension to 25 and 50 MHz. Multiple simultaneous 10 MHz pulses.

MW-MW DR In Action 10 MHz sinc (14724 – 14734 MHz) DR On DR

MW-MW DR In Action 10 MHz sinc (14724 – 14734 MHz) DR On DR Off * DR pulse centered at 14729. 4 MHz (178 9 ← 177 10, A state, GS) Modulating peak at 15344. 3 MHz (179 8 ← 178 9, A state, GS) Each spectrum is 200 k shots with 2 ms FIDs (20 minutes of averaging).

Results from “coarse” MW-MW DR 50 MHz sinc (14704 – 14754 MHz) 25 MHz

Results from “coarse” MW-MW DR 50 MHz sinc (14704 – 14754 MHz) 25 MHz sinc (14717 – 14742 MHz) DR On DR Off * * Pulses centered at 14729. 4 MHz (178 9 ← 177 10, A state, GS) Also targets 14738. 0 MHz (178 9 ← 177 10, E state, GS) 15344. 3 MHz: 179 8 ← 178 9, A state, GS 15370. 8 MHz: 179 8 ← 178 9, E state, GS For 25 MHz, can wipe out A and E states simultaneously. Not enough power to get full modulation for E on 50 MHz DR pulse.

Multi-peak MW-MW DR Use frequency agility of AWG to simultaneously pump multiple peaks, then

Multi-peak MW-MW DR Use frequency agility of AWG to simultaneously pump multiple peaks, then check modulated peaks individually.

Pumping Multiple Peaks Pumped 4 peaks (all A), expecting 6 modulations. Saw 7! *

Pumping Multiple Peaks Pumped 4 peaks (all A), expecting 6 modulations. Saw 7! * * * Inadvertently also pumped E state at 14698 MHz (affected 17864). Could automate to hit top X intense peaks as routine part of data collection.

Summary and Future Work Extended and improved prior fits of Susskind and Mäder on

Summary and Future Work Extended and improved prior fits of Susskind and Mäder on GS and torsionally excited states. Verified GS fits with various DR measurements (all peaks studied with DR were not previously assigned). Future work: • Try to further refine E states for ntors = 1. • Chirp instead of sinc to decouple bandwidth and duration for broad pulses. • Automated DR measurements on intense features in spectrum.

Acknowledgments Noah Anderson (NCF ‘ 12) Brittany Gordon (NCF ‘ 13) Erin Kent (NCF

Acknowledgments Noah Anderson (NCF ‘ 12) Brittany Gordon (NCF ‘ 13) Erin Kent (NCF ‘ 13) Morgan Mc. Cabe (NCF ’ 14) Maria Phillips (NCF ‘ 13) New College of Florida (Start-up funding) Research Corporation (Cottrell College Science Award) ACS Petroleum Research Fund (UNI Award) National Science Foundation (MRI-R 2 Award)

MW – MW Double Resonance First pulse polarizes transitions over a large bandwidth. Second

MW – MW Double Resonance First pulse polarizes transitions over a large bandwidth. Second pulse selectively pumps a single transition. This destroys coherences of connected levels, modulating intensity. 1 1 2 2

XIAM • Rho axis method • Recompiled up to J=99 • Used AABS for

XIAM • Rho axis method • Recompiled up to J=99 • Used AABS for GUI with several Python scripts • Fit rigid rotor parameters (including distortion) and four internal rotational parameters: – V 3 = 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 51 a, 923 -932 (1996). Z. Kisiel, L. Pszczolkowski, I. R. Medvedev, M. Winnewisser, F. C. De Lucia, C E. Herbst, J. Mol. Spectrosc. 233, 231 -243 (2005).

Noise Levels and Linewidths Peak FWHM is ~700 k. Hz, almost entirely due to

Noise Levels and Linewidths Peak FWHM is ~700 k. Hz, almost entirely due to 4 ms FID. Data are interpolated and splined. Peak centers are good to about 75 k. Hz.

Spectrum: Signals and Noise

Spectrum: Signals and Noise

Multi-sinc DR Pulses: 1) 14690. 6 MHz (189 9 ← 188 10, A state,

Multi-sinc DR Pulses: 1) 14690. 6 MHz (189 9 ← 188 10, A state, GS) 2) 14729. 4 MHz (178 9 ← 177 10, A state, GS) 3) 15661. 8 MHz (106 5 ← 105 6, A state, GS) 4) 16592. 2 MHz (116 6 ← 115 7, A state, GS) Should Modulate: 1) 17853. 4 MHz (188 10 ← 187 11, A state, GS) 2) 15344. 3 MHz (179 8 ← 178 9, A state, GS) 3) 15988. 0 MHz (105 6 ← 104 7, A state, GS) 3) 17680. 2 MHz (107 4 ← 106 5, A state, GS) 4) 17614. 1 MHz (117 5 ← 116 6, A state, GS) 4) 18040. 3 MHz (115 7 ← 114 8, A state, GS) Also close to: which modulated: 14698. 2 MHz (189 9 ← 188 10, E state, GS), 17863. 9 MHz (188 10 ← 187 11, E state, GS)

Tentative Additional Excited State Fit Parameters Current Previous [1] A (MHz) 3376. 42(3) 3367.

Tentative Additional Excited State Fit Parameters Current Previous [1] A (MHz) 3376. 42(3) 3367. 41 B (MHz) 2205. 77(3) 2199. 58 C (MHz) 1312. 09(3) 1314. 44 ΔJ (k. Hz) 3. 3(7) – ΔJK (k. Hz) -9. 6(4) – ΔK (k. Hz) 6. 0(3) – δJ (k. Hz) 0. 60(6) – δK (k. Hz) -5. 1(2) – Jmax 17 6 Nlines 21 (A only) 16 (A only) 96 140 sfit (k. Hz) Far too few lines to trust distortion constants. Really want to find E states to understand what’s going on. [1] Susskind, J. Chem. Phys. , 53, 2492 (1970).

Calculations at B 3 LYP/6 -311++G(d, p) Calculated barrier: 204. 7 cm-1 | m.

Calculations at B 3 LYP/6 -311++G(d, p) Calculated barrier: 204. 7 cm-1 | m. A | = 0. 97 D | m. B | = 1. 06 D Energy (cm-1) Rotation-Vibration Coupling Constants Description a. A (MHz) a. B (MHz) a. C (MHz) 92. 3 13. 37 -2. 47 1. 18 Methyl torsion 174. 4 7. 7 0. 99 -0. 85 Out-of-plane bend 269. 1 4. 5 -0. 94 -1. 06 Out-of-plane bend 283. 6 -4. 77 -1. 69 1. 06 In-plane bend

Effects of Internal Rotation E Rigid Molecule A Or High Barrier E Intensity A

Effects of Internal Rotation E Rigid Molecule A Or High Barrier E Intensity A Frequency Magnitude of splitting is related to barrier height. Frequency