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Recent developments in infra-red solar spectroscopy.

1948; Institute of Physics; Volume: 54; Linguagem: Inglês

10.1086/106155

1538-3881

Robert R. McMath, Orren C. Mohler, L. Goldberg,

Spectroscopy and Laser Applications

Since the late fall of 1947, the ~cGregor tower of the McMath-Hulbert Observatory has been used for study of the infra-red solar spectrum beyond the photographic limit. A specially designed, all-mirror optical system and Pfund-type grating spectrometer, with monochromator, have been used in conjunction with a Cashman leadsulphide cell to obtain direct-intensity tracings of the solar spectrum over the entire region between 8ooo and 25000 A. The spectrum is re corded on a scale of about five millimeters per angstrom. In the 15000 X region, lines with separation of 0.3 angstroms are just resolved. Water vapor absorption almost completely obliterates the spectrum in the regions I .3-1.5 microns and 1.75-1.95 microns. The intervening portions of the spectrum, however, are relatively clear and contain a wealth of solar atomic lines, as well as telluric molecular lines and bands. Progress in identification has been slow, largely because of the complete absence of high-resolution laboratory studies in this region of the infra-red spectrum. Approximately 200 solar atomic lines have been identified in the infra-red spectrum on the basis of wave lengths computed from known atomic energy levels. The elements for which lines have been found include Fe, Si, Na, AIg, Al, C, Ca, as well as the third and seventh members of the Brackett series of hydrogen. The vast majority of these lines have excitation potentials higher than five volts. Band systems of molecules originating in the earth's atmosphere constitute some of the most interesting features of the infra-red spectrum. Among these are four CO1 bands in the 1.6 micron region, which have been resolved for the first time, and three strong bands of CO1 at 2.1 microns. Among the identified molecular bands, those of ammonia and methane are particularly noteworthy. The evidence for ammonia as a constituent of the earth's atmosphere is very strong, while the evidence for methane is conclusive. Mc Math- Hulbert Observatory, Pontiac, Mich. and University of Michigan Observatory, Ann Arbor, Mich.