The Pure Rotational Spectrum of The Pure Rotational Spectrum of Pivaloyl Chloride, (CHPivaloyl Chloride, (CH33))33CCOCl, CCOCl,

between 800 and 18800 MHz.between 800 and 18800 MHz.Garry S. Grubbs IIGarry S. Grubbs II, Christopher T. Dewberry, , Christopher T. Dewberry, Kerry C. Etchison, Michal M. Serafin Kerry C. Etchison, Michal M. Serafin aa, Sean , Sean

A. Peebles A. Peebles aa, and Stephen A. Cooke, and Stephen A. Cooke

Department of Chemistry, The University of Department of Chemistry, The University of North Texas, PO Box 305070, Denton, TX, North Texas, PO Box 305070, Denton, TX,

USA, 76203USA, 76203

a a Visiting Professor and Student from the Visiting Professor and Student from the Department of Chemistry, Eastern Illinois Department of Chemistry, Eastern Illinois

University, 600 Lincoln Ave, Charleston, IL, USA, University, 600 Lincoln Ave, Charleston, IL, USA, 6192061920

IntroductionIntroduction Previous structural Previous structural

studies of some other studies of some other simple acyl chlorides simple acyl chlorides show the acyl chloride show the acyl chloride lying in the lying in the abab plane plane1,21,2

Durig and co-workersDurig and co-workers33 report a barrier of report a barrier of internal rotation for internal rotation for pivaloyl chloride studied pivaloyl chloride studied in the far-infrared regionin the far-infrared region

Test our Spectrometers!Test our Spectrometers!

PivalaldehydePivalaldehyde Very close structurally to pivaloyl chlorideVery close structurally to pivaloyl chloride Shows extensive internal rotation with a Shows extensive internal rotation with a

barrier of 337 cmbarrier of 337 cm-1-1 as reported by Durig as reported by Durig and co-workersand co-workers33

Rotational splittings of pivalaldehyde are Rotational splittings of pivalaldehyde are about 50 kHz in about 50 kHz in bb-type transitions -type transitions according to Cox according to Cox et al et al 44

Barrier to internal rotation is 807 cmBarrier to internal rotation is 807 cm-1-1 for for pivaloyl chloride as reported by the Durig pivaloyl chloride as reported by the Durig workwork33

Pivaloyl ChloridePivaloyl Chloride Interested in nuclear Interested in nuclear

quadrupole coupling quadrupole coupling constants, internal constants, internal rotational splitting, and rotational splitting, and quantum number quantum number assignmentassignment

Ab InitioAb Initio calculations calculations predict a highly asymmetric predict a highly asymmetric molecule with C-Cl bond molecule with C-Cl bond distance of 1.81 distance of 1.81 ǺǺ

cc-type transitions should be -type transitions should be weak (if they even exist)weak (if they even exist)

ExperimentExperiment Large dipole moment, high Large dipole moment, high

volatility and expected volatility and expected spectral density makes spectral density makes pivaloyl chloride a good pivaloyl chloride a good candidate for newly developed candidate for newly developed Search Accelerated, Correct Search Accelerated, Correct Intensity Fourier Transform Intensity Fourier Transform Microwave (SACI-FTMW) Microwave (SACI-FTMW) SpectrometerSpectrometer

As shown, can be coupled As shown, can be coupled with the highly sensitive Balle-with the highly sensitive Balle-Flygare techniqueFlygare technique

Setup is a derivative of the Setup is a derivative of the Chirped Pulse Fourier Chirped Pulse Fourier Transform Microwave Transform Microwave (CP-FTMW) Spectrometer (CP-FTMW) Spectrometer developed by Pate and developed by Pate and Co-workersCo-workers55

Picture taken from Grubbs [6].

SACI-FTMWSACI-FTMW

Based on the previously introduced Chirped Based on the previously introduced Chirped Pulse Fourier Transformed Microwave (CP-Pulse Fourier Transformed Microwave (CP-FTMW) Spectrometer introduced by Pate and FTMW) Spectrometer introduced by Pate and co-workersco-workers55

Range of spectrometer is 8 – 18 GHz Range of spectrometer is 8 – 18 GHz Has capability of observing up to 4 GHz regions Has capability of observing up to 4 GHz regions

at a timeat a time Spectra produced is an overlay of a scan up to 2 Spectra produced is an overlay of a scan up to 2

GHz above and below a center frequencyGHz above and below a center frequency

ExperimentExperiment High precision High precision

measurements were measurements were also performed on a also performed on a low-frequency low-frequency resonator capable of resonator capable of tuning below 2 GHztuning below 2 GHz

The small rotational The small rotational constants predicted constants predicted made study of low made study of low transitions in the Q and transitions in the Q and R branches possibleR branches possible

Figure taken from Etchison [7].

ExperimentExperiment

A Balle-Flygare spectrometer (circuit design by Grabow) A Balle-Flygare spectrometer (circuit design by Grabow) with coaxial sample source was used to measure with coaxial sample source was used to measure transitions in the 4 – 8 GHz range and to resolve some transitions in the 4 – 8 GHz range and to resolve some hyperfine splitting observed in the SACI-FTMW hyperfine splitting observed in the SACI-FTMW experiment.experiment.88 Picture taken from reference 8. Picture taken from reference 8.

Spectrometer SummarySpectrometer Summary

800 MHz 18800 MHz 4000 MHz 8000 MHz

Low-Frequency Resonator (can possibly go lower)

SACI-FTMW Spectrometer

Balle-Flygare Spectrometer (up to 26 GHz)

All of the measurements performed at the All of the measurements performed at the University of North TexasUniversity of North Texas

ExperimentExperiment

Passed 2-3 Passed 2-3 atmospheres of atmospheres of argon over and argon over and through a sample of through a sample of 98% pure pivaloyl 98% pure pivaloyl chloride through a chloride through a Parker-HannifinParker-Hannifin® ® Series 9 nozzle with Series 9 nozzle with a .030 in orificea .030 in orifice

ResultsResults

Two samples of spectra obtained for pivaloyl chloride Two samples of spectra obtained for pivaloyl chloride after 10,000 averaging cycles (~2.5 hrs)after 10,000 averaging cycles (~2.5 hrs)

Frequency (MHz)

250 450 650 850 1050 1250

Pivaloyl Chloride offset from 10900 MHz

Offset from 10900 MHz Offset from 14500 MHz

Frequency MHz

250 450 650 850 1050 1250 1450

14500 MHz Offset

ResultsResults Sample spectrum of Sample spectrum of

pivaloyl chloride in the pivaloyl chloride in the low-frequency low-frequency resonatorresonator

Transition is the 2Transition is the 21111, ,

7/2 7/2 ← 2← 21212, 7/2 for the , 7/2 for the 3535Cl isotope after 300 Cl isotope after 300 averaging cycles averaging cycles measured at measured at 835.1896(10) MHz835.1896(10) MHz

ResultsResults

The The 3535Cl 6Cl 61616 – 5 – 51515

transitions for transitions for pivaloyl chloride pivaloyl chloride observed on the observed on the Balle-Flygare Balle-Flygare experimentexperiment

AnalysisAnalysis

Relative intensities provided by the SACI-Relative intensities provided by the SACI-FTMW spectrometer eased spectrum FTMW spectrometer eased spectrum assignmentassignment

Line fitting was performed on Pickett’s Line fitting was performed on Pickett’s SPFIT programSPFIT program99

Watson A-reduction type Hamiltonian Watson A-reduction type Hamiltonian usedused1010

AnalysisAnalysis  Ab Initio 35Cl 35Cl 37Cl

A /MHz  2983.7  2977.99378(82)  2973.53738(65)

B /MHz 1722.4  1708.71195(33)   1671.393907(267)

C /MHz 1435.9  1430.038196(182)   1402.807756(136)

ΔJ /kHz   0.1536(39)   0.14132(296)

ΔJK /kHz   0.7695(287)   0.8045(231)

ΔK /kHz   -0.537(154)   -0.816(127)

δJ /kHz   0.03284(253)   0.02792(175)

δK /kHz   -1.8076(257)   -1.837(36)

Χaa /MHz -30.28  -33.1906(29)   -26.8353(23)

Χbb-Χcc /MHz -9.20 -11.78216(500)   -8.61228(400)

Χcc /MHz 19.74  22.48638(501)   17.72381(401)

Χab /MHz 39.38  43.590(245)   33.789(295)

Transitions   170   130

Δνrms /kHz   16.4  14.5 

SummarySummary The spectrum of pivaloyl chloride between The spectrum of pivaloyl chloride between

800 and 18800 MHz has been observed 800 and 18800 MHz has been observed and reportedand reported

Rotational Constants, Distortion Constants Rotational Constants, Distortion Constants and Nuclear Quadrupole Coupling and Nuclear Quadrupole Coupling Constants have been calculated and Constants have been calculated and reportedreported

No internal rotation observedNo internal rotation observed No No cc-type transitions observed-type transitions observed Calculated asymmetry parameter of Calculated asymmetry parameter of ≈ -0.6≈ -0.6

ReferencesReferences1. K. M. Sinnott, J. Chem. Phys. 34, 851 (1961).

2. H. Karlsson, J. Mol. Struct. 33, 227 (1976).

3. J. R. Durig, R. Kenton, H. V. Phan, and T. S. Little, J. Mol. Struct. 247, 237 (1991).

4. A. P. Cox, A. D. Couch, K. W. Hillig II, M. S. LaBarge, and R. L. Kuczkowski, J. Chem. Soc. Faraday Trans. 87, 2689 (1991).

5. G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, and B. H. Pate, J. Mol. Spec. 238, 200 (2006).

6. G. S. Grubbs II, C. T. Dewberry, K. C. Etchison, K. E. Kerr, and S. A. Cooke, Rev. Sci. Instr. 78, 096106 (2007).

7. K. C. Etchison, C. T. Dewberry, K. E. Kerr, D. W. Shoup, and S. A. Cooke, J. Mol. Spec. 242, 39 (2007).

8. K. C. Etchison, C. T. Dewberry, and S. A. Cooke, Chem. Phys. 342, 71 (2007).

9. H. M. Pickett, J. Mol. Spectrosc. 148, 371 (1991).

10. J. K. G. Watson, Vibrational Spectra and Structure 6, 1 (1977).

AcknowledgementsAcknowledgements I would like to thank all members of the I would like to thank all members of the

Cooke Group for their contributions to this Cooke Group for their contributions to this workwork

I would like to thank Dr. Sean Peebles and I would like to thank Dr. Sean Peebles and Eastern Illinois University for all their Eastern Illinois University for all their contributions to this workcontributions to this work

Funding and Support from University of Funding and Support from University of North Texas, a PRF administered by the North Texas, a PRF administered by the ACS and a Ralph E. Powe Junior Faculty ACS and a Ralph E. Powe Junior Faculty Enhancement GrantEnhancement Grant