Infrared spectroscopy astronomy

It will be clear from this subsection that much skillful and imaginative instrument design, by a number of different groups, has been directed towards the development of far-infrared spectroscopy. Quite apart from the developments in laboratory spectroscopy, the impact on astronomy in this region of the spectrum is of major importance. A high power tunable far-infrared source can serve as the local oscillator for the detection of far-infrared interstellar radiation. We can anticipate exciting developments in this field. 

Analytical Chemistry Collision-Induced Spectroscopy Hydrogen Bond Infrared Spectroscopy Interstellar Matter Ion Kinetics and Energetics Microwave Communications Millimeter Astronomy Quantum Chemistry Time... 

Cosmic Radiation Galactic Structure and Evolution Infrared Spectroscopy Interstellar Matter Planetary Satellites, Natural Solar System, General Stellar Spectroscopy Stellar Structure and Evolution Ultraviolet Space Astronomy... 

Nevertheless the heat capacity of a carbon resistor was not so low as that of crystalline materials used later. More important, carbon resistors had an excess noise which limited the bolometer performance. In 1961, Low [61] proposed a bolometer which used a heavily doped Ge thermometer with much improved characteristics. This type of bolometer was rapidly applied to infrared astronomy as well also to laboratory spectroscopy. A further step in the development of bolometers came with improvements in the absorber. In the early superconducting bolometer built by Andrews et al. (1942) [62], the absorber was a blackened metal foil glued to the 7A thermometer. Low s original bolometer [61] was coated with black paint and Coron et al. [63] used a metal foil as substrate for the black-painted absorber. A definite improvement is due to J. Clarke, G. I. Hoffer, P. L. Richards [64] who used a thin low heat capacity dielectric substrate for the metal foil and used a bismuth film absorber instead of the black paint. 

Rotational spectroscopy and microwave astronomy are the most accurate way to identify a molecule in space but there are two atmospheric windows for infrared astronomy in the region 1-5 im between the H2O and CO2 absorptions in the atmosphere and in the region 8-20 xrn. Identification of small molecules is possible by IR but this places some requirements on the resolution of the telescope and the spacing of rotational and vibrational levels within the molecule. The best IR telescopes, such as the UK Infrared Telescope on Mauna Kea in Hawaii (Figure 3.13), are dedicated to the 1-30 xm region of the spectrum and have a spatial resolution very close to the diffraction limit at these wavelengths. 

Fourier transform methods have revolutionized many fields in physics and chemistry, and applications of the technique are to be found in such diverse areas as radio astronomy [52], nuclear magnetic resonance spectroscopy [53], mass spectroscopy [54], and optical absorption/emission spectroscopy from the far-infrared to the ultraviolet [55-57]. These applications are reviewed in several excellent sources [1, 54,58], and this section simply aims to describe the fundamental principles of FTIR spectroscopy. A more theoretical development of Fourier transform techniques is given in several texts [59-61], and the interested reader is referred to these for details. 

In Astronomy. For detection of nebulae and stars otherwise invisible because of astronomic.tl haze or because their radiation lies chiefly in the infrared in infiared spectroscopy, for the determination of the composition, the temperature, and the movement of stars and nebulae. 

We have already discussed the high-resolution spectroscopy of the OH radical at some length. It occupies a special place in the history of the subject, being the first short-lived free radical to be detected and studied in the laboratory by microwave spectroscopy. The details of the experiment by Dousmanis, Sanders and Townes [4] were described in section 10.1. It was also the first interstellar molecule to be detected by radio-astronomy. In chapter 8 we described the molecular beam electric resonance studies of yl-doubling transitions in the lowest rotational levels, and in chapter 9 we gave a comprehensive discussion of the microwave and far-infrared magnetic resonance spectra of OH. Our quantitative analysis of the magnetic resonance spectra made use of the results of pure field-free microwave studies of the rotational transitions, which we now describe. 

Dense molecular clouds, often also called dark clouds, block entirely the light of stars which lie behind them, and can therefore be studied observationally only by radio astronomy or infrared techniques. These clouds have a visual extinction in excess of A 10 which corresponds to a gas density of n lO cm" and a kinetic temperature usually well below T 100 K, typically between 10 and 25 K. Within the last ten years, the investigation of these dark molecular clouds has become almost entirely the domain of radio astronomy although now the first very promising results by infrared astronomy reveal the power of this new branch of spectroscopy. 

There are several books reviewing IR spectroscopy for the instructor s background information. Mampaso et al have compiled an advanced and up-to-date review appropriately called Infrared Astronomy 28). The... 

Extension material to support this unit is available on our website. Case Study 4 on the website contains an article on Spectroscopy and Astronomy, covering many of the principles discussed in this unit. The infrared spectrum of car exhaust is shown on page 415. 

Infrared Astronomy Infrared TTchnology Macromolecules, Structure Microwave Molecular Spectroscopy Radiometry and Photometry Raman Spectroscopy... 

Source.-Lutz, D., eta/.. Probing starbursts with ISO mid-IR spectroscopy, /nExtragalactic Astronomy in the Infrared, MPI fur extraterrestrische Physik. 

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