Transcript ohio 2008.ppt

The Pure Rotational Spectrum of
Pivaloyl Chloride, (CH3)3CCOCl,
between 800 and 18800 MHz.
Garry S. Grubbs II, Christopher T. Dewberry,
Kerry C. Etchison, Michal M. Serafin a, Sean
A. Peebles a, and Stephen A. Cooke
Department of Chemistry, The University of
North Texas, PO Box 305070, Denton, TX,
USA, 76203
a Visiting
Professor and Student from the
Department of Chemistry, Eastern Illinois
University, 600 Lincoln Ave, Charleston, IL, USA,
61920
Introduction

Previous structural
studies of some other
simple acyl chlorides
show the acyl chloride
lying in the ab plane1,2
 Durig and co-workers3
report a barrier of
internal rotation for
pivaloyl chloride studied
in the far-infrared region
 Test our Spectrometers!
Pivalaldehyde
 Very
close structurally to pivaloyl chloride
 Shows extensive internal rotation with a
barrier of 337 cm-1 as reported by Durig
and co-workers3
 Rotational splittings of pivalaldehyde are
about 50 kHz in b-type transitions
according to Cox et al 4
 Barrier to internal rotation is 807 cm-1 for
pivaloyl chloride as reported by the Durig
work3
Pivaloyl Chloride



Interested in nuclear
quadrupole coupling
constants, internal
rotational splitting, and
quantum number
assignment
Ab Initio calculations
predict a highly
asymmetric molecule
with C-Cl bond distance
of 1.81 Ǻ
c-type transitions should
be weak (if they even
exist)
Experiment



Large dipole moment, high
volatility and expected
spectral density makes
pivaloyl chloride a good
candidate for newly developed
Search Accelerated, Correct
Intensity Fourier Transform
Microwave (SACI-FTMW)
Spectrometer
As shown, can be coupled
with the highly sensitive BalleFlygare technique
Setup is a derivative of the
Chirped Pulse Fourier
Transform Microwave
(CP-FTMW) Spectrometer
developed by Pate and
Co-workers5
Picture taken from Grubbs [6].
SACI-FTMW

Based on the previously introduced Chirped
Pulse Fourier Transformed Microwave (CPFTMW) Spectrometer introduced by Pate and
co-workers5
 Range of spectrometer is 8 – 18 GHz
 Has capability of observing up to 4 GHz regions
at a time
 Spectra produced is an overlay of a scan up to 2
GHz above and below a center frequency
Experiment

High precision
measurements were
also performed on a
low-frequency
resonator capable of
tuning below 2 GHz
 The small rotational
constants predicted
made study of low
transitions in the Q and
R branches possible
Figure taken from Etchison [7].
Experiment

A Balle-Flygare spectrometer (circuit design by Grabow)
with coaxial sample source was used to measure
transitions in the 4 – 8 GHz range and to resolve some
hyperfine splitting observed in the SACI-FTMW
experiment.8 Picture taken from reference 8.
Spectrometer Summary
800 MHz
4000 MHz
Low-Frequency Resonator
(can possibly go lower)
8000 MHz
18800 MHz
SACI-FTMW Spectrometer
Balle-Flygare Spectrometer (up to 26 GHz)
 All
of the measurements performed at the
University of North Texas
Experiment
 Passed
2-3
atmospheres of
argon over and
through a sample of
98% pure pivaloyl
chloride through a
Parker-Hannifin®
Series 9 nozzle with
a .030 in orifice
Results

Two samples of spectra obtained for pivaloyl chloride
after 10,000 averaging cycles (~2.5 hrs)
14500 MHz Offset
Pivaloyl Chloride offset from 10900 MHz
250
450
650
850
1050
Frequency (MHz)
Offset from 10900 MHz
1250
250
450
650
850
1050
1250
Frequency MHz
Offset from 14500 MHz
1450
Results
 Sample
spectrum of
pivaloyl chloride in the
low-frequency
resonator
 Transition is the 211,
7/2 ← 212, 7/2 for the
35Cl isotope after 300
averaging cycles
measured at
835.1896(10) MHz
Results
616 – 515
transitions for
pivaloyl chloride
observed on the
Balle-Flygare
experiment
 The 35Cl
Analysis
 Relative
intensities provided by the SACIFTMW spectrometer eased spectrum
assignment
 Line fitting was performed on Pickett’s
SPFIT program9
 Watson A-reduction type Hamiltonian
used10
Analysis
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
Summary
 The
spectrum of pivaloyl chloride between
800 and 18800 MHz has been observed
and reported
 Rotational Constants, Distortion Constants
and Nuclear Quadrupole Coupling
Constants have been calculated and
reported
 No internal rotation observed
 No c-type transitions observed
 Calculated asymmetry parameter of ≈ -0.6
References
1. 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).
Acknowledgements
I
would like to thank all members of the
Cooke Group for their contributions to this
work
 I would like to thank Dr. Sean Peebles and
Eastern Illinois University for all their
contributions to this work
 Funding and Support from University of
North Texas, a PRF administered by the
ACS and a Ralph E. Powe Junior Faculty
Enhancement Grant