Why diamond is transparent to infra red radiation?

Answer 1

absorption of IR radiation depends on a shift in the dipole vector (fancy way of saying "change in polarity"). think of it this way: IR radiation induces vibrations in bonds between atoms. if the dipole vector (the thing that looks like this: +-----> when your prof draws it out) doesn't change direction or magnitude, then the IR radiation will pass through without being absorbed. diatomic nitrogen similarly doesn't absorb in the UV (thus it isn't a green house gas) because there's no dipole vector (because it's not a polar molecule) and without a dipole vector it can't change [there is no dipole vector because there the two N atoms have identical electronegativity].

if this doesn't make sense, look up the definition for a dipole vector on wikipedia and see why it doesn't exist in a diamond lattice or in diatomic N2. seriously... chem profs looooove to ask about which molecules are IR active. keep in mind though, that some nonpolar molecules that don't have dipole vectors (because they're zero) are IR active because these molecules' polarity changes (the direction/magnitude of the DV changes).

incidentally, a tetrahedron has bond angles at 109.5 degrees and not 90. definitely don't write that down on a test. good luck.

Answer 2

I'm sure it's because the carbon atoms are set in a tetrahedral crystal structure. I think all the bonds are at 90 degrees and are single bonds.

It's a very simple very stable structure if the crystal has no impurities.

Answer 3

I thought they were transparent in any kind of light.

Answer 4

idk