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Explain singlet, duplet and triplet energy terms in electronic spectra
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Singlet, doublet, and triplet energy terms in electronic spectra refer to the spin multiplicity of the electronic states involved in transitions.
Singlet state: All electron spins are paired, resulting in a total spin of S=0. This state is designated as 1 (2S+1 = 1).
Doublet state: One unpaired electron, leading to a total spin of S=1/2. This state is designated as 2 (2S+1 = 2).
Triplet state: Two unpaired electrons with parallel spins, resulting in a total spin of S=1. This state is designated as 3 (2S+1 = 3).
The spin multiplicity influences the selection rules for electronic transitions. Transitions between states with different spin multiplicities are typically forbidden, leading to weaker or absent spectral bands. For example, transitions from a singlet ground state to a triplet excited state (singlet-triplet transitions) are spin-forbidden and usually have very low intensity.
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