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Liquid Sulfur 105 of formation their relative concentrations at the melting point and the boil- ing point of sulfur have been calculated as follows (related to the concentra- tion of species 1) [109]: – At 393 K (melting point): – 1:2:3:4:5:6:7:8:9= 1 : 2104 : 2104 : 1104 : 3106 : 4107 : 11011 : 31012 : 71018 – At 718 K (boiling point): – 1:2:3:4:5:6:7:8:9= 1 : 9103 : 9103 : 6103 : 1103 : 3104 : 1106 : 5107 : 41010 Branched long chains of the type -S-S-S(=S)-S-S- must also be compo- nents of the polymeric S1 present in liquid sulfur at higher temperatures since the model compound H-S-S-S(=S)-S-S-H was calculated to be by only DGo298=51 kJ mol1 less stable at the G3X(MP2) level than the helical isomer of hexasulfane, H2S6 [109]. Isomeric forms of cyclo-S6 and cyclo-S7 can also be suspected as compo- nents of liquid sulfur at high temperatures. However, their relative energies have not been calculated yet on a high enough level of theory to obtain real- istic concentrations. The reflectance spectra of solidified liquid sulfur previously equilibrated at temperatures of between 120 and 440 C have been measured at 25 C and color pictures of these solidified melts were published [112]. These data are used to explain the yellow, orange and red colors of the sulfur flows on Jupi- ters moon Io on which a number of very active sulfur volcanoes have been discovered [113]. These volcanoes are powered by SO2 gas which forces the liquid sulfur from its underground deposits to the surface. If hot sulfur melts or hot vapors at low pressure are condensed at low temperatures highly colored samples are obtained which may be black, green or red depending on the temperature and pressure conditions and the rate of quenching. These colors originate from the small molecules and radi- cals present at high temperatures and which are trapped in the solid sample. At room temperature these samples turn yellow, or—if not—the sulfur has not been pure. 3.4 Photochemistry of Liquid Sulfur The photochemistry of elemental sulfur has been studied using solid, liquid and dissolved sulfur rings as well as solid polymeric sulfur. The general out- come is that the absorption of photons of sufficient energy triggers a ho- molytic bond dissociation with formation of free radicals as well as a break- down of S8 rings into smaller singlet molecules like S3+S5 or two S4. In liquid solutions photochemical interconversion as well as polymerization reactions of sulfur homocycles are observed [114]. In the case of liquid sulfur only very few investigations are available. Sakaguchi and Tamura [115] illuminat-PDF Image | Topics in Current Chemistry
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