Question

If the spin of the electrons in the excited state are parallel, it is called as:

• A. Doublet state
• B. Triplet state
• C. Singlet state
• D. Parallel state

Answer 1

The Correct Option is B

The correct option is (B): Triplet state.

Answer 2

The multiplicity of an electronic state in spectroscopy is determined by the total spin of the electrons involved and is calculated as (2S+1), where S is the total spin quantum number. Each option can be checked against this rule as applied to a molecule with two electrons, one in the ground orbital and one excited:

1. Doublet state: A doublet state arises from a system with a single unpaired electron (total spin S=1/2, giving multiplicity 2), which describes species like free radicals, not the two-electron excited/ground orbital pair being discussed here.
2. Triplet state: When the excited electron's spin becomes parallel to the spin of the electron remaining in the lower orbital, the two unpaired electron spins add up to a total spin S=1, giving a multiplicity of (2×1+1)=3. A state with multiplicity three is called a triplet state, and this is exactly the situation of parallel spins described in the question.
3. Singlet state: A singlet state occurs when the two electrons remain spin-paired (antiparallel), giving a total spin S=0 and multiplicity (2×0+1)=1. This is the opposite spin arrangement to the parallel-spin case being asked about.
4. Parallel state: This is not an established term used in spectroscopic state nomenclature; multiplicity-based states are named singlet, doublet, triplet and so on according to the (2S+1) rule, not "parallel state."

Since parallel electron spins give a total spin of one and hence a multiplicity of three, the correctly named state is the triplet state.

Therefore, the correct answer is Triplet state.