The key difference between singlet and triplet state is that the singlet state shows only one spectral line whereas triplet state shows a threefold splitting of spectral lines.
The terms singlet and triplet states are discussed under quantum mechanics. We can describe these terms regarding the spin of the system, i.e. atom. In quantum mechanics, spin is not a mechanical rotation. It is a concept that characterizes a particle’s angular momentum.
CONTENTS
1. Overview and Key Difference
2. What is Singlet State
3. What is Triplet State
4. Side by Side Comparison – Singlet State vs Triplet State in Tabular Form
5. Summary
What is Singlet State?
A singlet state refers to a system in which all the electrons are paired. The net angular momentum of the particles in this type of system is zero. Therefore, we can say that the overall spin quantum number, s is zero (s=0). Furthermore, if we take the spectrum of this system, it shows one spectral line, and thus, got the name “singlet state”. Moreover, almost all the molecules that we know exist in the singlet state, but molecular oxygen is an exception.
Figure 1: Comparing Singlet, Doublet and the Triplet States
As an example, the simplest possible bound particle pair having singlet state is positronium, which has an electron and positron. These two particles are bound by their opposite electrical charge. Moreover, the paired electrons of a system having a singlet state have parallel spin orientations.
What is Triplet State?
Triplet state of a system describes that the system has two unpaired electrons. The net angular momentum of the particles in this type of system is 1. Therefore, the spin quantum number is 1. Moreover, this allows three values of the angular momentum as -1, 0 and +1. Hence, the spectral lines that we obtain for this type of system split into three lines, and thus, got the name triplet state.
Shown are three electronic configurations of the molecular orbitals of molecular oxygen, O2. From left to right, the diagrams are for: 1Δg singlet oxygen (first excited state), 1Σ+ g singlet oxygen (second excited state), and 3Σ− g triplet oxygen (ground state).
Furthermore, the best example of a triplet state is molecular oxygen. At room temperature, this molecular oxygen gives threefold splitting in the spectral lines.
What is the Difference Between Singlet and Triplet State?
A singlet state refers to a system in which all the electrons are paired. Whereas, the triplet state of a system describes that the system has two unpaired electrons. The key difference between singlet and triplet state is that singlet state shows only one spectral line whereas triplet state shows the threefold splitting of spectral lines.
Moreover, a further difference between singlet and triplet state is that the spin quantum number of a singlet state is s=0 while it is s=1 for a triplet state. Besides, almost all the molecules that we know exist in singlet state except for the molecular oxygen. Whereas, molecular oxygen occurs at triplet state.
Below info-graphic summarizes the difference between singlet and triplet state.
Summary – Singlet vs Triplet State
We can discuss the terms singlet state and triplet state as facts about minute systems such as atoms. The key difference between singlet and triplet state is that the singlet state shows only one spectral line whereas triplet state shows the threefold splitting of spectral lines.
Reference:
- “Triplet State.” Wikipedia, Wikimedia Foundation, 16 Feb. 2019.
- “Singlet State.” Wikipedia, Wikimedia Foundation, 27 Dec. 2018.
Image Courtesy:
- “Spin multiplicity diagram” By Llightex – Own work, CC BY-SA 4.0, via Commons Wikimedia
- “Two singlet excited states and triplet ground state of molecular dioxygen” By Angelo Frei – Own work, CC BY-SA 3.0, via Commons Wikimedia