Transcript PhilMorgan_p078.ppt

High Resolution Electronic
Spectroscopy of p-Vinylphenol in the
Gas Phase
Philip J. Morgan, Diane M. Mitchell,
and David W. Pratt
Department of Chemistry
University of Pittsburgh
Pittsburgh, PA 15260
Objectives
• Resolve controversy concerning thermal
decomposition of p-coumaric acid
• Assignment of origin bands to respective
conformations
• Set foundation for future work
p-Coumaric Acid Conformers
trans-pCA
cis-pCA
Fluorescence Excitation Spectrum
*Taken from Ryan et al. J. Am. Chem. Soc. 2002, 124, 6194-6201.
Low Resolution Apparatus
Mirror
Dye
Laser
Nd3+:YAG
Laser
Filter
Vacuum
Chamber
Iris
PMT
KDP
Crystal
h
He
Boxcar
Integrator
Computer
Low Resolution Spectrum
4
Band I
Intensity
3
2
Band II
1
0
33150
33250
33350
33450
33550
33650
Frequency (cm-1)
33750
33850
33950
34050
High Resolution Apparatus
240 m
nozzle
High Resolution Spectra
4
Intensity
3
2
1
0
33150
33250
33350
33450
33550
33650
33750
33850
33950
34050
Frequency (cm-1)
Band I
1.6 cm-1
Band II
1.5 cm-1
Fit of Band I
33205.9
33205.9
cm-1
cm-1
~0.07 cm-1
33208.1
33208.1
Fit of Band II
33210.2
33210.2
cm-1
cm-1
~0.07 cm-1
33213.0
33213.0
Inertial Parameters
A" (MHz)
B" (MHz)
C" (MHz)
Experimental
Band II
Band I
5031.8(2)
5024.4(5)
988.9(1)
989.6(1)
827.7(1)
828.0(1)
*Calculated values done at MP2/3-21G level of theory
Theoretical
trans-pCA
3449.1
344.8
321.0
Thermal Decarboxylation
∆
• According to de Groot and Buma, thermal
decarboxylation occurs to produce pVP
Conformers of p-Vinylphenol
c
c
a
a
b
b
trans-pVP
cis-pVP
Inertial Parameters
A" (MHz)
B" (MHz)
C" (MHz)
∆A (MHz)
∆B (MHz)
∆C (MHz)
Experimental
Theoretical
Band I
Band II trans-pVP cis-pVP
5024.4(5) 5031.8(2)
4973.8
4979.9
989.6(1) 988.9(1)
992.2
991.6
828.0(1) 827.7(1)
833.6
834.1
-257.2(5) -268.9(2)
-152.7
-162.0
14.8(1)
15.7(1)
28.0
30.0
2.4(1)
2.6(1)
8.4
8.8
*Calculated values done at MP2/6-31G** and CIS/6-31G** levels of theory
Conclusions
• Carrier of bands have been attributed to
p-vinylphenol
– Agreement with de Groot and Buma
• Bands I & II have been assigned to
trans-pVP and cis-pVP, respectively
Future Endeavors
trans-pCA oxyester
cis-pCA oxyester
*LIF spectrum of pCA oxyester supplied by Buma et al.
Acknowledgements
Dr. David Pratt
The Pratt Group Members:
Leonardo Alvarez
Jessica Thomas
Inertial Parameters
A" (MHz)
B" (MHz)
C" (MHz)
∆ I" (amu Ǻ2)
∆A (MHz)
∆B (MHz)
∆C (MHz)
∆I ' (amu Ǻ2)
a/b/c type
Origin (cm-1)
Experimental
Band I
Band II
5024.4(5)
5031.8(2)
989.6(1)
988.9(1)
828.0(1)
827.7(1)
-0.902
-0.874
-257.2(5)
-268.9(2)
14.8(1)
15.7(1)
2.4(1)
2.6(1)
-0.560
-0.457
65/35/0
65/35/0
33207.3
33211.8
Theoretical
trans-pVP
cis-pVP
4973.8
4979.9
992.2
991.6
833.6
834.1
-4.7
-5.2
-152.7
-162.0
28.0
30.0
8.4
8.8
-0.0001
-0.0005
*Calculated values done at MP2/6-31G** and CIS/6-31G** levels of theory
Molecular Orbitals
trans-pVP
homo-1
cis-pVP
homo
lumo
lumo+1
Inertial Parameters
A" (MHz)
B" (MHz)
C" (MHz)
∆A (MHz)
∆B (MHz)
∆C (MHz)
Experimental
Theoretical
Theoretical
Experimental
Theoretical
Band II
Band
trans-pVP
cis-pVP
Band II
II trans-pVP
trans-pVP cis-pVP
5024.4(5)
4979.9
4973.8
4979.9
5024.4(5) 5031.8(2)
5031.8(2) 4973.8
989.6(1)
992.2
991.6
992.2
991.6
989.6(1) 988.9(1)
988.9(1)
991.6
828.0(1)
833.6
834.1
833.6
834.1
828.0(1) 827.7(1)
827.7(1)
834.1
-257.2(5)
-152.7
-162.0
-152.7
-162.0
-257.2(5) -268.9(2)
-268.9(2)
14.8(1)
15.7(1)
28.0
30.0
28.0
30.0
14.8(1)
15.7(1)
30.0
2.4(1)
2.6(1)
8.4
8.8
8.4
8.8
2.6(1)
*Calculated values done at MP2/6-31G** and CIS/6-31G** levels of theory
High Resolution Apparatus
Beam Machine
Molecular Beam, Source and Collection Optics
Energy Level and Transitions
S1
V’=0
S0
With a narrow-band UV laser,
we are able to observe
transitions between rotational
levels in the ground and the
excited electronic states.
UV 35,000 cm-1
V”=1
V”=0
IR 3500 cm-1
MW ~1cm-1