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| Titel |
An upper limit for water dimer absorption in the 750 nm spectral region and a revised water line list |
| VerfasserIn |
A. J. L. Shillings, S. M. Ball, M. J. Barber, J. Tennyson, R. L. Jones |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 9 ; Nr. 11, no. 9 (2011-05-09), S.4273-4287 |
| Datensatznummer |
250009703
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| Publikation (Nr.) |
 copernicus.org/acp-11-4273-2011.pdf |
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| Zusammenfassung |
Absorption of solar radiation by water dimer molecules in the Earth's
atmosphere has the potential to act as a positive feedback effect for
climate change. There seems little doubt from the results of previous
laboratory and theoretical studies that significant concentrations of the
water dimer should be present in the atmosphere, yet attempts to detect
water dimer absorption signatures in atmospheric field studies have so far
yielded inconclusive results. Here we report spectral measurements in the
near-infrared around 750 nm in the expected region of the | 0⟨f | 4⟩b|0 ⟩
overtone of the water dimer's hydrogen-bonded OH
stretching vibration. The results were obtained using broadband cavity
ringdown spectroscopy (BBCRDS), a methodology that allows absorption
measurements to be made under controlled laboratory conditions but over
absorption path lengths representative of atmospheric conditions. In order
to account correctly and completely for the overlapping absorption of
monomer molecules in the same spectral region, we have also constructed a
new list of spectral data (UCL08) for the water monomer in the 750–20 000 cm−1
(13 μm–500 nm) range.
Our results show that the additional lines included in the UCL08 spectral
database provide an improved representation of the measured water monomer
absorption in the 750 nm region. No absorption features other than those
attributable to the water monomer were detected in BBCRDS experiments
performed on water vapour samples containing dimer concentrations up to an
order of magnitude greater than expected in the ambient atmosphere. The
absence of detectable water dimer features leads us to conclude that, in the
absence of significant errors in calculated dimer oscillator strengths or
monomer/dimer equilibrium constants, the widths of any water dimer
absorption features present around 750 nm are of the order of 100 cm−1
HWHM, and certainly greater than the 25–30 cm−1 HWHM reported in the
literature for lower energy water dimer transitions up to 8000 cm−1. |
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