When it comes to the movement of electrons between different energy levels within an atom, certain rules apply. These rules, known as spectroscopy selection rules, identify some radiative electronic transitions as forbidden. For example, it is commonly stated that the single electron of a hydrogen atom cannot move from S2 to S1, or from P2 to S2 (and vice versa) with photon emission or absorption.
But what about collisional (or, more generally, radiationless) transitions? Are there any selection rules that apply here?
The Wigner Spin Conservation Rule
One rule that does apply to collisional electronic transitions is the Wigner spin conservation rule. This rule states that in any collision process, the total spin projection of the system must be conserved. In simpler terms, this means that if the spin of an electron changes in a collision, then the spin of another particle involved in the collision must also change.
To understand this rule better, let’s consider an example. Suppose we have two identical atoms, each with one valence electron in a p orbital. When these atoms collide, the total spin projection of the system must be conserved. If one of the electrons changes its spin from up to down, then the other electron must also change its spin from down to up in order to maintain total spin projection.
The Wigner spin conservation rule is of great importance in understanding the behavior of electron collisions in many different systems.
Other Selection Rules?
While the Wigner spin conservation rule is a fundamental rule that applies to many collisional electronic transitions, there may be other selection rules that apply in specific situations.
These rules are often dependent on the geometry of the system in question, as well as other factors such as the polarizability of the electrons involved. In some cases, these rules may restrict certain electronic transitions from occurring altogether.
Conclusion
So, are there any forbidden collisional electronic transitions? The answer is not a simple yes or no. While the Wigner spin conservation rule is a fundamental law that applies to many different systems, there may be other selection rules that come into play in specific situations.
Overall, understanding the behavior of electrons in different collisional systems can help us better understand the behavior of matter on a microscopic level.
Are There Any Forbidden Collisional Electronic Transitions?
When it comes to the movement of electrons between different energy levels within an atom, certain rules apply. These rules, known as spectroscopy selection rules, identify some radiative electronic transitions as forbidden. For example, it is commonly stated that the single electron of a hydrogen atom cannot move from S2 to S1, or from P2 to S2 (and vice versa) with photon emission or absorption.
But what about collisional (or, more generally, radiationless) transitions? Are there any selection rules that apply here?
The Wigner Spin Conservation Rule
One rule that does apply to collisional electronic transitions is the Wigner spin conservation rule. This rule states that in any collision process, the total spin projection of the system must be conserved. In simpler terms, this means that if the spin of an electron changes in a collision, then the spin of another particle involved in the collision must also change.
To understand this rule better, let’s consider an example. Suppose we have two identical atoms, each with one valence electron in a p orbital. When these atoms collide, the total spin projection of the system must be conserved. If one of the electrons changes its spin from up to down, then the other electron must also change its spin from down to up in order to maintain total spin projection.
The Wigner spin conservation rule is of great importance in understanding the behavior of electron collisions in many different systems.
Other Selection Rules?
While the Wigner spin conservation rule is a fundamental rule that applies to many collisional electronic transitions, there may be other selection rules that apply in specific situations.
These rules are often dependent on the geometry of the system in question, as well as other factors such as the polarizability of the electrons involved. In some cases, these rules may restrict certain electronic transitions from occurring altogether.
Conclusion
So, are there any forbidden collisional electronic transitions? The answer is not a simple yes or no. While the Wigner spin conservation rule is a fundamental law that applies to many different systems, there may be other selection rules that come into play in specific situations.
Overall, understanding the behavior of electrons in different collisional systems can help us better understand the behavior of matter on a microscopic level.