Lecture 3

Question 1

Why can’t we just consider spin momenta for lanthanides?

Answer 1

• 4f orbitals are core like and shielded from 5s and 5p electrons
• can no longer assume that angular momentum is quenched

Question 2

What scheme is used and how is it defined?

Answer 2

• Russel Saunders coupling
• S = total spin
• L= total orbital
• J = L+S,…L-S

Question 3

When is Russell-Sunders coupling appropriate

Answer 3

• when spin orbit coupling is weak in comparison to electron-electron repulsion

Question 4

What is used when spin orbit coupling is large in comparison to ligand field effects?

Answer 4

• Term symbols
• S is maximised
• The highest value of L is the lowest in energy
• For a shell that is less than half-filled J is as low as possible
• For a shell that is more than half-filled J is as high as possible

Question 5

What do term symbols assume?

Answer 5

• only the Ground state is populated

- true for Ln3+ ions

Question 6

What do Ln electronic spectra look like?

Answer 6

• all similar and independent of ion environment
• spin rules are not relaxed as in TM due to contracted 4f orbitals not interacting with ligands
• Sharp transitions
• less intense colours

Question 7

UV-Vis spectra of Ln

Answer 7

• intense absorptions

- due to allowed 4f to 5d transitions

Question 8

Ln Fluorescence

Answer 8

• F-F relaxation

- particularly favoured by Eu 3+ and Tb 3+ as their excited states are below the typical triplet states of ligands

Question 9

Magnetic properties of Actinides

Answer 9

• complex
• large spin orbit coupling but ligand effects are comparable due to extended 5f orbitals
• J values are split by the ligand field
• Ueff varies with temp

Question 10

Electronic spectra of actinides

Answer 10

• increased vibronic coupling
• broader and more intense peaks
• more intense colours
• later actinides represent Ln3+ more
• colours become paler across the series