What is the Difference Between Singlet and Triplet State?

🆚 Go to Comparative Table 🆚

The main difference between singlet and triplet states lies in the number of unpaired electrons and their stability. Here are the key differences:

  • Singlet State: A singlet state refers to a system in which all electrons are paired. The net angular momentum of the particles in this type of system is zero, resulting in an overall spin quantum number of s=0. Singlet states are lower in energy than triplet states and are more common in most molecules encountered in daily life.
  • Triplet State: A triplet state describes a system with two unpaired electrons. This state is higher in energy than the singlet state and is more stable due to the presence of two unpaired electrons. Triplet states are less common than singlet states, with molecular oxygen being a notable exception.

In summary, singlet states have all electrons paired, resulting in a lower energy and higher stability, while triplet states have two unpaired electrons, making them higher in energy and less stable than singlet states.

Comparative Table: Singlet vs Triplet State

The difference between singlet and triplet states lies in the electron spin configurations and their corresponding energy levels. Here is a comparison of the two states:

Property Singlet State Triplet State
Spin Configuration All electrons are paired with opposite spins (one spin up and one spin down) At least two unpaired electrons, leading to two possible configurations: parallel spins (↑↑) and antiparallel spins (↓↓)
Orbital Configuration The electrons are paired in the same orbital The electrons can be in different orbitals
Spin Angular Momentum (S) S = 0 S = 1
Energy Level Lower energy Higher energy
Spectral Line Appearance Single spectral line (the origin of the term "singlet") Triplet splitting of spectral lines, often resulting in three separate lines
Occurrence in Molecules Many molecules exist in the singlet state, except for a few special cases like molecular oxygen (O2) Properly bonded molecules can exist in the triplet state, but transitions to this state are usually forbidden and rare

In summary, singlet states are characterized by paired electrons with opposite spins, while triplet states have at least two unpaired electrons with parallel or antiparallel spins. Singlet states typically have lower energy levels compared to triplet states, and their spectral line appearances are also distinct.