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Atmospheric RadiationTheoretical Basis$
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R. M. Goody and Y. L. Yung

Print publication date: 1989

Print ISBN-13: 9780195051346

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195051346.001.0001

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Vibration-Rotation Spectra of Gaseous Molecules

Vibration-Rotation Spectra of Gaseous Molecules

(p.67) 3 Vibration-Rotation Spectra of Gaseous Molecules
Atmospheric Radiation

R. M. Goody

Y. L. Yung

Oxford University Press

In this chapter we discuss the characteristics of absorption by gaseous constituents of the earth’s atmosphere. This is a complex topic and atmospheric investigators may be disturbed by the idea that weather and climate might be affected by details of the kind we shall discuss. But, as yet, we lack criteria as to what is important and what is not, leaving little alternative to developing a general understanding of the field. A full description of the atmospheric absorption spectrum involves the intensities, state dependence, and detailed line profiles of 105 to 106 lines of 20 or more different chemical species. Given the capabilities of modern computers, it is possible to store, retrieve, and manipulate such data and this is the method of choice for purposes such as the identification of lines in high-resolution spectra. One of a number of current attempts to assemble an up-to-date archive of molecular data is the Air Force Geophysics Laboratory (AFGL) magnetic tape. Not only does this tape provide an economical means of access to the best data from a vast literature, but it also provides a convenient international standard atmosphere. Two numerical climate models, both using the AFGL data, cannot attribute their differences to the radiation data employed. We shall, therefore, address the subject of molecular spectroscopy in the general context of the AFGL tape and many of our illustrations are composed from the tape in preference to seeking out observed spectra. As will be apparent by the end of this chapter, it may sometimes take an expert to distinguish between the two. Figure 3.1 offers an overview of the atmospheric absorption spectrum. The six gases considered are the most important radiators, although climate studies often involve more and rarer species. All six gases are minor species (and therefore in dilute mixtures with nitrogen and oxygen) and are very simple molecules (methane is the most complex). Figure 3.1 shows no visible or ultraviolet spectra. The missing features are mainly electronic bands of oxygen and ozone; they will not be treated in this chapter since they are more complex theoretically but easier to handle empirically than the bands shown in Fig. 3.1.

Keywords:   ATC theory, Band intensity, Collision diameter, Dimers, Electric field, Fermi resonance, Ground-state band, Hamiltonian operator, Inertia tensor

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