Cometary spectroscopy

There were also several experiments involving current topics that did not fit neatly into a category. These included studies of supercritical phenomena (140, 141), cometary spectroscopy (142), experimental studies on the thermodynamics of heat pumps (143), a study of industrially relevant phase transfer catalysts (144), and finally an electrochemical study of a commercial soap (145). Both the environmental and the miscellaneous experiments can be found listed in Table X. 

The hydroxyl radical, OH, occupies an extremely important position in spectroscopy, in free radical laboratory chemistry, and in atmospheric, cometary and interstellar chemistry. Its ultraviolet electronic spectrum has been described in many papers published over the past seventy years. It was the first short lived gaseous free radical to be studied by microwave spectroscopy, described in a classic paper by Dousmanis, Sanders and Townes [121] in 1955. The details of this work are presented in chapter 10. It was the first free radical to be studied by microwave magnetic resonance, in pioneering work by Radford [141] the microwave and far-infrared laser magnetic resonance studies are... 

Carbonates are common in hydrous meteorites and hydrous IDPs, where they are believed to have formed by parent-body aqueous processing. Since simple models of cometary evolution involve no aqueous processing, carbonates were generally presumed not to occur in comets. However, carbonates have also been detected by infrared spectroscopy in the dust shell around evolved stars and in protostars, where liquid water is not expected (Ceccarelli et al. 2002 Kemper et al. 2002). Indeed, Toppani et al. (2005) have performed experiments that indicate that carbonates can be formed by non-equilibrium condensation in circumstellar environments where water is present as vapor, not as liquid. Detections of carbonates in other exosolar systems are reported by Ceccarelli et al. (2002) and Chiavassa et al. (2005). 

The recent ai roach of large comets such as IP/Halley, C71996 B2 Hyakutake, and C/1995 Ol Hale-Bopp to the Earth provided a good opportunity to investigate the detailed composition of cometary ices by various methods such as mass spectrometry, infrared spectroscopy, and radio emission. The composition of interstellar ices is compared with that of the cometary ices in Table 9.3. It is striking that cometary and interstellar ices have quite comparable relative molecular abundances. 

Moroz, L.V. Arnold, G. Korochantsev, A.V. Wasch, R. Natural solid bitumens as possible analogs for cometary and asteroid organics 1. Reflectance spectroscopy of pure bitumens. Icarus 1998, 134, 253-268. 

Radio astronomy of comets has made its most significant advances in the area of spectroscopy. Many so-called parent molecules (molecules which sublimate directly off the nucleus, in contrast to daughter molecules, which are products of the parents) have been observed at radio wavelengths through their rotation lines in the millimeter and submillimeter bands. Observations of these spectral lines give valuable information on the icy composition of the cometary nucleus, gas production rates, physical conditions in coma, and variation of these in time and heliocentric distance. 

---