# Definition of t2g orbitals in CFT

My textbook defines $$\mathrm{t_{2g}}$$ orbitals as

$$\mathrm{t_{2g}}$$ stands for a set of three orbitals which are asymmetric with respect to $$C_2$$ axes, perpendicular to the highest $$C_n$$ axes, but which is symmetric in sign through the centre of inversion.

I know that “$$\mathrm{t}$$” is a randomly chosen letter as suggested by M. Farooq, “$$\mathrm{g}$$” comes from gerade (MOT), that's what the last line says. Though “$$2$$” in subscript must have come from $$C_2$$, but I didn't get the meaning of

…which are asymmetric with respect to $$C_2$$ axes, perpendicular to the highest $$C_n$$ axes.

Please explain what does this line conveys.

• I have checked the original literature, t or T, does not stand for three or triplet. It was a randomly chosen letter. You are right g is for gerade. In original works, the letter F was used alphabetically, A,B,E, F as symmetry labels. Jan 2, 2020 at 5:28
• Dos this answer your question: What are t2g and eg in CFT? Jan 2, 2020 at 8:39
• @andselisk But this post does not include the above definition or it's meaning. Wasn't the meaning of "t, e, g" explained in broader essence? Jan 2, 2020 at 11:30
• @M.Farooq what is the original literature for this? I had always assumed the symmetry labels had some German connection.
– Tyberius
Jan 3, 2020 at 14:37
• Tyberius, actually not. I was planning to write a short historical article. Except for g and u I could not authenticate any other German meaning. The rest are mostly myths including $Entartet$ for degenerate. Jan 3, 2020 at 15:03