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WIREs Comput Mol Sci
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Accurate variational calculations for line lists to model the vibration–rotation spectra of hot astrophysical atmospheres

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The first principles calculation of the spectra of small molecules is making a significant impact on high‐resolution spectroscopy as well as astrophysics and atmospheric physics. Variational nuclear motion calculations, combined with high‐accuracy ab initio electronic structure computations, are being used to make spectral predictions of increasing accuracy with very few a priori assumptions. This work is important for spectral analysis and particularly for dipole transition intensities, which are often very difficult to measure reliably but are essential inputs for many applications such as modeling of radiative transport and remote sensing. Demands for very extended line lists covering many, many millions of transitions which are required to simulate spectra of hot sources are best met using high‐quality theoretical models. This aspect of the use of variational nuclear motion calculations is discussed with reference to both the benchmark water molecule and future data needs, in particular, for models of the atmospheres of extrasolar planets. © 2011 John Wiley & Sons, Ltd.

Figure 1.

Schematic figure showing the steps in a first principles calculation of the rotation–vibration spectrum of a molecule.

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Figure 2.

Photometry and spectroscopy data for the Hot–Jupiter exoplant HD189733b recorded with multiple instruments and teams using Spitzer and Hubble Space Telescope (points with error bars), as well as ground‐based instruments. The curve is a simulated emission spectrum containing H2, H2O, CH4, and CO2. (G. Tinetti, private communication (2010), based on data given in Ref 97.)

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Figure 3.

Temperature‐dependent spectrum of hot water as a function of wavelength in μm. Note that the absorption intensity, given in units of cm−1/(molecule cm−2), is plotted on a logarithmic scale. (After Ref 102.)

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Figure 4.

Room temperature comparison of laboratory measured spectrum of ammonia, as taken from the HITRAN database,110 with the line list calculated using the program ‘TROVE’. (Reprinted with permission from Ref 98. Copyright 2009 American Chemical Society.)

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Figure 5.

Laboratory absorption spectrum of water at 2900 K (dots)113 compared with available spectra synthesized by various line lists. The UCL line list BT2 gives the best results;114 other line lists are as specified in Table 2 (S. Tashkun, private communication, 2006).

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Theoretical and Physical Chemistry > Spectroscopy

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