Oxygen molecule melting point

Oxygen in the solid state consists of 02 molecules. From 24 K to 43.6 K they are packed as in a-F2. Under pressure (5.5 GPa) this packing is also observed at room temperature. Below 24 K the molecules are slightly tilted against the hexagonal layer. From 43.6 K up to the melting point (54.8 K) the molecules rotate in the crystal as in /3-F2. Under pressure oxygen becomes metallic at approximately 100 GPa, but it remains molecular. 

Potassium chlorate, KCIO3, is a colorless, crystalline material with a melting point of 640 K. Just above the melting-point temperature, it decomposes to produce oxygen molecules according to ... 

The characteristic melting points and IR frequencies of 55 indicate well-defined compounds. The second molecule HX in the salts d, d, e, e is probably firmly included, forming hydrogen bonds to the available oxygen atoms. These salts are easily obtained and should be versatile building blocks in solid-state reactions or reactions in dry aprotic solvents [9]. 

The water solubility of R-(EO)n types of nonionic emulsifiers is derived from the weak interaction between the ether oxygen of EO unit and water. It was suggested that each EO unit in the PEO chain, requires three molecules of water to form a hydrated complex [35]. This hydrogen bond complex is destroyed if the solution is taken above the melting point of the PEO. Water usually acts as plasticizer when present in hydrophilic PEO polymers and Tg values decrease with increasing water contents [36]. This phenomenon in the PEO-water system is observed up to 1 mol water/ether group. Beyond this a rise in Tg is observed and water acts as an antiplasticizer. 

The big difference in melting points suggests a difference in type of crystal binding. The intermolecular forces in solid CO2 must be very low to be overcome by a low-temperature sublimation. CO2 is actually a molecular lattice held together only by the weak van der Waals forces between discrete CO2 molecules. Si02 is a covalent lattice with a three-dimensional network of bonds each silicon atom is bonded tetrahedrally to four oxygen atoms and each oxygen is bonded to two silicon atoms. 

Reactivity of carbon-centered radicals may remain high even in crystalline state of the matrix when the access of oxygen towards unpaired electrons is not hindered by the sterical arrangement of surrounding molecules. This is, e.g., the case of peroxyl radicals formed during irradiation of cholesterol [60]. Oxygen reacts with alkyl radicals derived from cholesterol already at 125 K which is far below the melting point of the matrix (423 K). Two peroxyl radicals of cholesterol were observed (Scheme). 

---