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Collisional parameters of H2O lines: effect of temperature

Wagner, Georg and Birk, Manfred and Gamache, R.R. and Hartmann, J.-M. (2005) Collisional parameters of H2O lines: effect of temperature. Journal of Quantitative Spectroscopy and Radiative Transfer, 92, 211-230doi:10.1016/j.jqsrt.2004.07.023.

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Abstract

High resolution Fourier transform spectra of H2O-air mixtures have been measured at 296, 742, and 980 K for total pressures of 0.5 and 1.0 atm in the region of the ƒÞ2 band. From these recordings, air-broadening coefficients have been determined for the doublet lines with Kc=J. From these data and previous experimental determinations, line-broadening parameters ƒ×(T) are obtained at all three temperatures for the doublet lines from J=0 up to J=16. These values are then used to deduce the temperature dependence exponent n, such that . The values of n obtained using the two elevated temperatures are consistent and show that line widths decrease with T for small J values (n „l +0.8), are almost temperature independent on T for J„l10, and increase with T for high J lines (n „l -0.3 for J„l15). This original result, which confirms theoretical predictions made about fifteen years ago with a semi-classical approach [J Chem Phys 1987;86:144-56], is analyzed here using an improved version of the model. Comparisons between measured and computed widths show that calculations cannot reproduce correctly the experimental results at all temperatures simultaneously. This failure is attributed to the use of an inappropriate interaction potential and to the very strong dependence of the broadening ƒ×(v) on the relative velocity v for high J lines. This strong variation of ƒ×(v) raises the question, which is discussed, of what calculated quantity is to be compared with measured values (i.e. , (T), or some other more complex mean to account for the velocity averaging of the spectral profile itself?). Nevertheless, when the temperature exponent n is considered, satisfactory agreement between experiments and predictions is obtained, particularly when the averaging of widths over the relative velocity distribution is made.

Document Type:Article
Additional Information: LIDO-Berichtsjahr=2005,
Title:Collisional parameters of H2O lines: effect of temperature
Authors:
AuthorsInstitution or Email of Authors
Wagner, GeorgUNSPECIFIED
Birk, ManfredUNSPECIFIED
Gamache, R.R.UNSPECIFIED
Hartmann, J.-M.UNSPECIFIED
Date:2005
Journal or Publication Title:Journal of Quantitative Spectroscopy and Radiative Transfer
Refereed publication:Yes
In ISI Web of Science:Yes
Volume:92
Page Range:211-230doi:10.1016/j.jqsrt.2004.07.023
Status:Published
Keywords:water vapor, infrared, pressure broadening, high temperature
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):UNSPECIFIED
Location: Oberpfaffenhofen
Institutes and Institutions:Remote Sensing Technology Institute
Deposited By: Cornelia Roehl
Deposited On:17 Feb 2006
Last Modified:06 Jan 2010 22:41

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