low lying vacant d orbital

low-lying = low-energy (comparing with the outermost filled orbitals)
vacant = empty (not filled)

In an atom, no matter how many electrons it has, there are a number of orbitals, i.e.
1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p ......

Among these orbitals, only some of them are filled, but most of them are empty.
For example, in a ground-state hydrogen atom, only 1s orbital is filled with one electron, and all other orbitals are vacant.

Example 1: fluorine (ground state)
F: 1s^2 2s^2 2p^5
Vacant d-orbitals include 3d, 4d, 5d ......
The filled outermost shell of F is the 2nd shell. All of the 3d, 4d, 5d ...... orbitals have much higher energy than the 2nd shell, and thus all of these d orbitals are say to be NOT low-lying. There are no low-lying vacant d-orbitals.

Example 2: chlorine (ground state)
F: 1s^2 2s^2 2p^6 3s^2 3p^5
Vacant d-orbitals include 3d, 4d, 5d ......
The filled outermost shell of Cl is the 3rd shell. The vacant 3d orbitals have similar energy levels comparable to the filled outermost 3s and 3p orbitals, and thus the 3d orbitals are said to low-lying. All of the other d orbitals, i.e. 4d, 5d ...... orbitals, have much higher energy than the 3rd shell, and they are say to be NOT low-lying.

2011-03-12 17:36:24 補充：
NOT only d-orbitals are low-lying.

For example, Mn: [Ar] 4s^2 5d^5
The 4p orbitals are also vacant and low-lying. In the formation of MnO4^- ion, one low-lying vacant 4p orbital of Mn is used.

老爺子
可不可以麻煩幫幫看這個關於d-orbitals are low-lying問題
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