Refraction, atomic oxygen

The physical and chemical properties of any material are closely related to the type of its chemical bonds. Oxygen atoms form partially covalent bonds with metals that account for the unique thermal stability of oxide compounds and for typically high temperatures of electric and magnetic structure ordering, high refractive indexes, but also for relatively narrow spectral ranges of transparency. 

The naturally occurring dioxide exists in three crystal forms anatase, rutile and brookite. While rutile, the most common form, has an octahedral structure. Anatase and brookite have very distorted octahedra of oxygen atoms surrounding each titanium atom. In such distorted octahedral structures, two oxygen atoms are relatively closer to titanium than the other four oxygen atoms. Anatase is more stable than the rutile form by about 8 to 12 kJ/mol (Cotton, F.A., Wilkinson, G., Murillo, C.A and M Bochmann. 1999. Advanced Inorganic Chemistry, 6 ed, p. 697, New York John Wiley Sons) Other physical properties are density 4.23g/cm3 Mohs hardness 5.8 g/cm ( anatase and brookite) and 6.2 g/cm ( rutile) index of refraction 2.488 (anatase), 2.583 (brookite) and 2.609 (rutile) melts at 1,843°C insoluble in water and dilute acids soluble in concentrated acids. 

In a similar way it is easy to show that a flat molecule or polyatomic ion (such as CO ion, in which all the atoms lie in a plane and the oxygen atoms form an equilateral triangle round the carbon atom) has a higher refractive index when the electric vector lies in the plane of the group of atoms than when it is perpendicular to this plane. 

In view of this, it is not surprising that neighbouring ions have only minor effects, since the distances between oxygen atoms in neighbouring ions are 2-7 A. Nor is it surprising that in crystals in organic substances, where the distances between linked carbon atoms are 1 3-1 5 A and the distances between carbon atoms in neighbouring molecules 3 5-4 2 A, the refractive indices depend almost entirely on the refractivities of individual molecules and the relative orientations of these molecules in the crystals. 

According to Briihl, the last representation is in closest agreement with the specific refraction of the gas, and it also gives at least as easy an explanation as the others of the readiness with which the ozone molecule eliminates one atom leaving a stable molecule of oxygen. 

Atomic refractivities of phosphorus in its compounds are calculated as the difference between the molar refractivities and the sums of the refractivities of the other atoms. They vary according to the structure assigned, namely, whether oxygen is to be considered as singly- or doubly-linked. Molar refractivities appear to be affected by con-... 

Consider 1-methylnaphthalene and 1-methoxynaphthalene, which differ by a single oxygen atom. The molar refractions, 48.8 cm3 and 55.4 crp, respectively, differ by 6.6 crn, while the normal atomic refraction of an ether oxygen is only 1.6 cm. ... 

MR-Ri exhibited the molar refractivity effect of only Ri-substituent. In Eq. 40, Id-02 is an indicator variable that was assigned a value of 1 for a molecule containing a heterocycling ring with two oxygen atoms. Obviously such a heterocyclic ring did not seem to be of advantageous. 

---