Selection Rules

rotational transitions in diatomic molecules gross selection rule

size and orientation of the dipole moment must change during the rotational transition so the molecule must have a permanent dipole

rotational transitions in diatomic molecules specific selection rule

ΔJ=±1

vibrational transition in diatomic molecules (IR) gross selection rule

Must be a change in the dipole moment of the molecule during the vibrational transition so diatomic molecules must have a permanent charge dipole

vibrational transition in diatomic molecules (IR) specific selection rule

Δv=±1

vibrational transition in polyatomic molecules (IR) gross selection rule

Must be a change in the dipole moment of the molecule during the vibrational transition but polyatomic molecules do not need a permanent charge dipole

vibrational transition in polyatomic molecules (IR) specific selection rule

Δv=±1, ±2, ±3…

vibrational transition in polyatomic molecules (Raman) specific selection rule

Δv=±1, ±2, ±3…

vibrational transition in polyatomic molecules (Raman) gross selection rule

polarizability must change during the vibrational transition

nuclear spin transitions specific selection rule

Δm_l= ±1

nuclear spin transitions gross selection rule

non-zero nuclear quantum spin number (l)