24 MolecularSpectra

Seitzman all rights reserved v1 r p v0 5 school

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Unformatted text preview: r Spectra -10 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. v=1 R P v=0 !"#$%$ 5 School of Aerospace Engineering Example CO IR Fundamental • Distinct P and R branches in fundamental band from C.N. Banwell, Fundamentals of Molec. Spectroscopy (1983) !"#$%$ Molecular Spectra -11 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. School of Aerospace Engineering CO Fundamental and 1st Overtone • v 1 (overtones) weaker • With lower resolution, bands appear primarily as two smoothed features 2 bumps: P and R bands merged together Fundamental Band (v=0 1) ~5 m 1st Overtone(v=0 2) ~2.2 m from C.N. Banwell, Fundamentals of Molec. Spectroscopy (1983) Molecular Spectra -12 We can see here that n ow we get emission a nd absorption at these wavelengths Copyright © 2009 by Jerry M. Seitzman. All rights reserved. !"#$%$ 6 School of Aerospace Engineering Here we're seeing more CO2 than CO with water because more vibrational modes Example: IR H2O, CO2 • Again, with reduced resolution can identify specific bands of each molecule Siegel and Howell (1981) from C.N. Banwell, Fundamentals of Molec. Spectroscopy (1983) !"#$%$ Molecular Spectra -13 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. School of Aerospace Engineering Atmospheric Absorption • Cold air absorption primarily due to H2O and CO2 in IR • O2 electronic transition in near IR (750 nm) • O3, O2, N2 absorption in UV and vacuum UV (below 190 nm) absorption/emission require dipole change in molecule + image from Wikipedia (solar spectrum.png) Molecular Spectra -14 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. like CO, CO2, H2O !"#$%$ O2, N2, too symetric and dipole cannot change and they cant absorb radiation 7 School of Aerospace Engineering Shock Heated Air – IR Emission • Very weak emission in near IR for – “pure” N2 – “pure” O2 • Increase in emission for air Has to be another species: – why? NO, or if we say there is a small a mount of CO2 and H2O Molecular Spectra -15 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. Wurster and Marrone, “Nitric oxide radiation in the near I.R. spectrum of shock-heated air,” JQSRT 7 (1967) !"#$%$ School of Aerospace Engineering High T Air Radiant Energy Sources Molecular Spectra -16 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. Siegel and Howell (1981) !"#$%$ 8 School of Aerospace Engineering Other Options for Calculating a • Narrow band models a(v) Ivb – absorption coefficient varies rapidly across spectral region, while other quantities (e.g., Ivb) do not – possible to substitute actual absorption coefficients with approximate values averaged over a “narrow” spectral range v • Wide band models – even across ro-vibronic band, Ivb does not vary substantially – integrate narrow band model over an entire band Molecular Spectra -17 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. !"#$%$ 9...
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