Quantum mechanics sets the rules for atomic transitions, determining which ones are allowed or forbidden. These govern the strength and appearance of , crucial for understanding atomic structure and interactions with light.
Transition probabilities and intensities depend on factors like wavefunctions and energy differences. Concepts like and help quantify transition strength, providing insights into atomic behavior and spectroscopic observations.
Transition Types and Rules
Allowed and Forbidden Transitions
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Allowed transitions occur when selection rules are satisfied
Allowed transitions result in strong spectral lines
Forbidden transitions violate selection rules
Forbidden transitions produce weak or absent spectral lines
Forbidden transitions can occur due to magnetic dipole or electric quadrupole interactions
decreases significantly for forbidden transitions
Selection Rules for Atomic Transitions
govern electric dipole transitions
Dipole selection rules include:
Change in : ΔL = ±1
Change in : ΔmL = 0, ±1
No change in : Δn can be any value
applies to centrosymmetric molecules and atoms
Laporte rule states transitions between states of the same parity are forbidden
Parity refers to the symmetry of the under inversion
restricts changes in spin
Spin selection rule states ΔS = 0 for singlet-singlet or triplet-triplet transitions
Transitions between singlet and triplet states (ΔS ≠ 0) are spin-forbidden
Transition Characteristics
Transition Probability and Intensity
Transition probability measures likelihood of a spectral transition
Transition probability depends on:
Initial and final state wavefunctions
Dipole moment operator
between states
quantifies spontaneous emission probability
describes stimulated emission and absorption probabilities
correlates with transition probability
Strong transitions have high probabilities and intense spectral lines
Weak transitions have low probabilities and faint or absent spectral lines
Oscillator Strength and Transition Dipole Moment
Oscillator strength measures transition strength
Oscillator strength relates to the transition dipole moment