EGAS41 - Swansea University

41 st EGAS CP 176 Gdańsk 2009
Cavity ring-down measurements of the line parameters of water
rotation-vibration transitions near 1.39 µm
D. Lisak 1,∗ , D.K. Havey 2 , J.T. Hodges 2
1 Instytut Fizyki, Uniwersytet Miko̷laja Kopernika,
ul. Grudziadzka 5/7, 87-100 Toruń, Poland
2 Process Measurements Division, National Institute of Standards and Technology,
100 Bureau Drive, Gaithersburg, Maryland 20899, USA
∗ Corresponding author: dlisak@fizyka.umk.pl
Water vapor dominates the absorption of incoming (solar) and outgoing (thermal) radiation
in the Earth’s atmosphere, and its rotation-vibration spectrum is relevant to remote
sensing techniques. In many applications, such as propulsion, combustion, ultra-high purity
gases for semiconductor manufacturing, particle synthesis, human breath analysis,
the measurement of water vapor amount via absorption spectroscopy provides essential
information for system quantification, control, and optimization. Moreover commercially
available and widely used optical hygrometers use water absorption transition near 1.39
µm.
In this study a low uncertainty line intensities and line shape parameters were measured
for rotation-vibration transitions of water vapor near 1.39 µm. High-resolution
absorption spectra of water vapor/nitrogen mixtures were acquired using the frequencystabilized
cavity ring-down spectrometer at the National Institute of Standards and Technology
[1]. The NIST primary standard humidity generator [2] was used to produce a
stable and accurately known amount of water vapor in a nitrogen carrier gas stream.
Line intensities and line shape parameters were determined for 15 water transitions perturbed
by nitrogen. A combination of semiclassical line shape models, which take into
account collisional broadening and shifting, as well as the collisional narrowing and the
speed-dependence of collisional effects, with a multi-spectrum fits of spectra measured
for different gas pressures allowed us to determine a set of line shape parameters which
are linear with pressure. The relative combined standards uncertainties of reported line
intensities are smaller than 0.4% in most cases. We also discuss the influence of the choice
of line shape model on fitted line intensities and line shape parameters. Our experimental
results are compared to experimental and theoretical data available in the literature.
Agreement between our experimental intensity measurements and those derived by recent
ab initio calculations of the dipole moment surface of water vapor is within 1.5% [3].
References
[1] J.T. Hodges and D. Lisak, Appl. Phys. B 85, 375 (2006)
[2] J.T. Hodges and G.E. Scace, Micro 24, 59 (2006)
[3] D. Lisak, D.K. Havey, J.T. Hodges, Phys. Rev. A, accepted (2009)
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