Infrared Diode Laser Spectroscopy of the ν 3 Fundamental Band of the PO 2 Free Radical.
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Transcript of Infrared Diode Laser Spectroscopy of the ν 3 Fundamental Band of the PO 2 Free Radical.
Infrared Diode Laser Spectroscopy of the ν3 Fundamental Band of the PO2 Free Radical
Michael Lawson
PN
OCH2CF3
O
O2NO
ONO2
n
PPZ-E
• Low glass transition temperatures
• Easy to modify physical properties
• “High Energy”
Energetic Polyphosphazenes
Are transient phosphorus species generated by the pyrolysis of energetic polyphosphazenes??
PN PO PO2 PNO
PN
O
O
Lead-Salt Diode Laser Spectroscopy of Transient Phosphorus Species
Chemiluminescence
Observed: - PN, PH, PO, P2O, PO2,PNO, BrPO, ClPO, cis-HOPO
Sensitivity: ~1010 molecules cm-3
Temporal resolution: ~ 1 ms.
Resolution: ~10-4 cm-1
Discreet modes < ~1 cm-1
Modes spread over ~100 cm-1
Fiddly to use
Diode Laser Spectrometer.
Laser is modulated at 10.5 kHz.
Lock-in amplifiers detect signal at 2f.
Spectrum is recorded as the laser current is slowly ramped.
PN
OCH2CF3
O
O2NO
ONO2
n
PPZ-E
• Low glass transition temperatures
• Easy to modify physical properties
• “High Energy”
Energetic Polyphosphazenes
Are transient phosphorus species generated by the pyrolysis of energetic polyphosphazenes??
PN PO PO2 PNO
Do we have enough sensitivity?
Chemically Generating the PO2 Radical
P4 + He (500mt)
Pump (140 l s-1)
O2 (200mT) + discharge
S/N Limited by pumping capacity
ν3 fundamental
Extra Lines?
Exp.
Calc.
ν3
724 lines were measured and assigned, of which 504 were “new” observations.
75% coverage of the v3 band using 3 diode lasers.
ν3
1348.06 1348.07 1348.08 1348.09 1348.1 1348.11 1348.12 1348.13 1348.14 (cm-1)
Global Fitting of PO2 v3 band
Exp.
Calc.
• Microwave/LMR lines for the ground state were combined with our lines and lines from a previous work that filled gaps in our spectra to give a total of 887 lines.
• V3 = 1 hyperfine parameters were constrained to the ground-state.
• Unresolved spin rotation lines were appropriately weighted and blended together.
• Microwave/LMR lines for the ground state were combined with our lines and lines from a previous work that filled gaps in our spectra to give a total of 887 lines.
• V3 = 1 hyperfine parameters were constrained to the ground-state.
• Unresolved spin rotation lines were appropriately weighted and blended together.
1348.06 1348.07 1348.08 1348.09 1348.1 1348.11 1348.12 1348.13 1348.14 (cm-1)
Global Fitting of PO2 v3 band
Exp.
Calc.
Exp.
Global Fitting of PO2 v3 band
All fitting carried out using the SPFIT program.
Results:
Microwave/LMR RMS: 44 kHz
Infrared RMS: 0.00061 cm-1
Global RMS: 0.00057 cm-1
Calc.
Rotational Constants
Quartic centrifugal distortion constants
Sextic centrifugal distortion constants
Parameter Ground state v3 = 1
A 3.4859780(12) 3.408325(15)
B 0.28680773(12) 0.2859092(14)
C 0.26422996(13) 0.2630608(13)
Parameter Ground state v3 = 1
ΔN x 106 0.15534(33) 0.1583(10)
ΔNK x 104 -0.129613(90) -0.12975(23)
ΔK x 103 0.95353(17) 0.90803(36)
δN x 107 0.33126(63) 0.3376(36)
δK x 105 0.1507(18) 0.139(13)
Parameter Ground state v3 = 1
εaa 0.054590(13) 0.053384(53)
εbb 0.0007171(11) 0.000620(70)
εcc -0.0014810(12) -0.001504(66)
Electron spin-rotation constants
Parameter Ground state v3 = 1
HN x 1011 0.0035(28) 0.016(29)
HNK x 109 -0.0400(86) -0.044(11)
HKN x 108 -1.072(26) -1.006(28)
HK x 106 0.8833(36) 0.8222(46)
hN x 1012 0.073(73) Constrained
hNK x 109 0.046(21) Constrained
Parameter Ground state v3 = 1
LK x 108 -0.0918(32) -0.0854(33)
Octic centrifugal distortion
Global Fit Results
Exp.
Calc.
Unassigned Lines
1314.8 1315 1315.2 1315.4 1315.6 1315.8 1316
Energy cm-1
Species Responsible for Unassigned Lines?
• Metastable Excited state of PO2?
• Another phosphorus oxide, PO3 P4O?• Relatively sparse lines density –> light with high
symmetry.
DFT(B3LYP)/6-311++G(d,p)
0 Energy (cm-1) 0.6
Summary
• Excellent method of generating PO2 in large quantities in a discharge flow cell.
• Recorded the spectrum of the PO2 ν3 fundamental band at Doppler-limited resolution.
• Produced a definitive set of spectroscopic constants improving the v3 line predications by up to an order of magnitude.
• Ruled out the unassigned lines as arising from the ν3 fundamental of PO2.
AcknowledgementsPaul Davies – Supervisor.
Kristian Hoffman - Taught me how to use the spectrometer.
Mike CasfordPeter Kett - Group members.
Phillip Martin - Allowed us to use his helium cold head.
Adrian King - Useful discussions about SPFIT and Gaussian 03.
AWE, Aldermaston -Sponsorship.
Thank you!