Resonance in electron impact on atoms

[vrinda mukund]

Can someone please explain the significance of resonance levels that forms when electron collides with atoms. How this resonance levels are different from other levels ?

 

[Simon Bridge]

You should be able to answer that from the meaning of "resonance".
Have a go, and then we' all be able to help you better.

 

[vrinda mukund]

@Simon Bridge

Dear Sir,

When two frequencies match together so that the system oscillates at larger amplitudes, we say the system is in resonance. My doubt is how it is applicable to excited levels. Are they the levels with the same value for angular momentum J ? I that case, what makes it so special or different from other excited states.
To be more elaborate on my problem :

Ground state of Xenon is 5s² 5p⁶
First excited state for Xenon will be 5p⁶ 6s¹
If we write the term symbols the there will be five states :
¹P₁ ³P₀ ³P₁ and ³P₂
Now, the states ¹P₁ and ³P₁ are resonance levels.
So what i have guessed is levels with same value for J are said to be resonance levels . Is it really so ? How is it different from other levels ³P₀ and ³P₂

 

[Simon Bridge]

When two frequencies match together so that the system oscillates at larger amplitudes, we say the system is in resonance.

... close:
If you make a plot of the amplitude vs driving frequency for a driven oscilator, you get a characteristic peak near the natural frequency of the oscillator. That peak is called "a resonance".

My doubt is how it is applicable to excited levels.

... in the case of electrons being shot at some atoms, what is the graph that would be plotted? What shape would it have?

 

[vrinda mukund]

For electron-atom collisions, we can make energy Vs Cross section plots. We can plot how the cross section of a particular reaction, say excitation, changes with increasing energy of incident electron. The cross section will first increase with increase in energy and then will fall down.

 

[Simon Bridge]

Well done - between the "increase" and "fall down" there is a peak; that peak is called a "resonance peak".
We say that the particular process that the cross-section is for has a resonance at the energy level of the peak.
That is basically the entire significance of "resonance" in this context.

 

[vrinda mukund]

In that case, in the example of Xenon, which i explained before, is it like, the excitation cross section for excitation to the 5p⁵ 6s¹ levels will be maximum when electrons are excited to ¹P₁ and ³P₁ states ?