june 19th 2012 160 math. annex atmos. spec. ta3 9:04 a.m simultaneous measurements of no 2 and its...

June 19th 2012 160 MATH. ANNEX Atmos. Spec. TA3 9:04 a.m

Simultaneous Measurements of NO2 and its Dimer N2O4 at Room Temperature with a Multiplexed Intra-pulse

Quantum Cascade

Laser Spectrometer Geoffrey Duxbury, David Wilson and Nigel LangfordDepartment of Physics (SUPA), University of Strathclyde, John Anderson Building, 107 Rottenrow, Glasgow, G4 0NG, UK [email protected]


Outline of Talk• Multiplexed Intra-pulse Quantum Cascade laser

spectrometer• Dimerisation of NO2 to N2O4

• FT infrared spectrum of N2O4 • Simultaneous measurements with and without

N2O4

• Expanded view of NO2-N2O4 QC laser spectra• Concentrations of NO2-N2O4 at room temperature• Summary


Spectrometer using pulsed quantum cascade lasers: Multiplex Method

• Apply a 1500 ns top hat current pulse to each DFB QC laser, with a time delay of the trigger pulses.

• Obtain a light pulse in time

domain with two separated frequency down chirps.

• Pass pulse through absorbing species and monitor pulse absorption in time domain.

• Laser and Vigo MCT detector both Peltier cooled, no liquid nitrogen needed

Layoutof QClasershoused in Cascade Technologies“Developer Heads”. Each witha ZnSe lens tocollimatethe outputbeam.


Multiplexed spectra, preset time delay between the two pulse generators for QC laser1 and QC laser 2.

Averaged output from Acqiris digitiser

LHS digitised output from Vigo detector, RHS Converted to transmission


Temperature dependence of the

N2O4 - NO2 systemCalculated temperature dependence of the N2O4 - NO2 equilibrium pressures for an overall pressure of 1 Torr.

After I.A. Leenson, J. Chemical Education 77, 1652-1655 (2000)


FTIR spectra of N2O4 the region of 11

Recorded at ULB and ETH


N2O4 11 band at 293.15 K(from Jean Vander Auwera, ULB)dh11, Sband = 5.93(64) (in 10-17 cm/molecule)

J. Quant. Spectrosc. Radiat Transfer 50, 595 (1993)


Absorbance spectra of NO2 recorded in the 1276 cm-1 region (a) and the 1343 cm-1 region (b)

Region (a) lies close to the 11 band of N2O4. The displacement of the baseline with pressure is evidence of overlap with the wing of the R branch of the 11 band.


Absorbance spectra of NO2 recorded higher gas pressures (a) 1276 cm-1 region and (b)

the 1343 cm-1 region

Note the increasing baseline shift with pressure in (a), and also the increasing number of sharp absorption features of N2O4. No baseline shifts are observed in (b)


Increased absorbance of the quasi-continuum associated with the 11 band of N2O4, as the scan is shifted towards

the N2O4 band centre.


Lowest wavenumber spectrum of NO2 using an operating temperature of 43 C

and a pulse length of 2 s.The lowest wavenumber achieved, 1270.1 cm-1, is approximately 9 cm-1

above the centre of the 11 band of N2O4,1261.1 cm-1.


Comparison of FTS and QCL 1 spectra at the high and low wavenumber regions of QCL 1

High wavenumber Low wavenumber


SummaryIn this paper we have shown that long duration pulse operation

of the recent generation of QC lasers provides a powerful tool for measuring complex spectra, such as those provided by the NO2 - N2O4 equilibrium. The resolution is similar to a high resolution Fourier transform spectrometer, see [1], and allows both sharp and broad absorption features to be measured simultaneously.

Comparison of two regions, one with overlapping NO2 and N2O4, the other with NO2 only, allows the equilibrium to be determined at a particular temperature. In a previous optical measurement of this equilibrium only the electronic spectrum of NO2

was used. (L. Harris and K.L. Churney, J. Chem. Phys. 47, 1703-1709 (1967)


[1] G. Duxbury N. Langford. K G. Hay and N. Tasinato, ”Quantum cascade laser spectroscopy: diagnostics to non-linear optics”, J. Mod. Opt, 56, 2034-2048 (2009)

[2] D. Hurtmans, M. Herman and J. Vander Auwera, “Integrated band intensities in N2O4 in the infrared range”, J. Quant. Spectrosc. Radiat. Transfer 50, 595-602 (1993)

[3] D. Luckhaus and M. Quack, “High-resolution FTIR spectra of NO2 and N2O4 in supersonic jet expansions and their rovibrational analysis”, Chem. Phys. Lett. 199, 293-301 (1992)

[4] M. Hepp, R. George, M. Herman, J.-M. Flaud and W.J. Lafferty, “Striking anharmonic resonances in N2O4: supersonic jet Fourier transform spectra at 13.3, 7.9, 5.7 and 3.2 m”, J. Mol. Struct., 517-518, 171-180, (2000)

[5] F. Melen, F. Pokorni and M. Herman,”Vibrational band analysis of N2O4” Chem. Phys. Lett., 194 181-186 (1992)[6] Y. Elyoussoufi, M. Herman, J. Lievin anf I. Kleiner, “Ab initio and experimental investigation of the vibrational

energy pattern in N2O4: the mid and near infrared ranges”, Spectrochim. Acta, A53, 881-894 (1997)

[7] A. Perrin, J.-Y. Mandin, C. Camy-Peyret, J.-M. Flaud, J.-P. Chevillard and G. Guelachvili, “ The 1 band of 14N16O2: Line positions and intensities”, J. Mol. Spectrosc. 103, 417-435 (1984)

[8] A. Perrin, J.-M. Flaud, C. Camy-Peyret, A.-M. Vasserot, G. Guelachvili, A. Goldman, F.J. Murcray and R.D. Blatherwick, “ The 1, 22 and 3 interacting bands of 14N16O2: Line positions and intensities.”, J. Mol. Spectrosc., 154, 391-406 (1992)

[9] L.S. Rothman et. al. “The HITRAN 2008 molecular spectroscopic database”, J. Quant. Spectrosc. Radiat.

Transfer. 110, 533-572 (2009)

References


Acknowledgements We are indebted to the EPSRC for for the award to David Wilson of a

studentship through the Doctoral Training Fund

GD is grateful to the Leverhulme Trust for the award of an Emeritus Followship

We would also like to thank the Jean Vander Auwera, and his colleagues at the ULB, Bruxelles, for providing the Fourier transform spectra of N2O4 used

in this presentation

june 19th 2012 160 math. annex atmos. spec. ta3 9:04 a.m simultaneous measurements of no 2 and its...

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