# What are the allowed transitions in the pure rotational spectra of CO2 molecule?

• Shivpal
In summary, the selection rule for \DeltaJ is +/- 1 in quantum mechanics. However, some calculations suggest that odd values of J are not allowed, resulting in only even J values being allowed for transitions. This contradicts the professor's statement and raises the question of the accuracy of their statements. Further research and confirmation is needed to determine the validity of the professor's claims.
Shivpal
I know that the selection rule is :
$$\Delta$$J = +/- 1

but our prof said that according to some quantum mechanical calculations the odd values of J are not allowed. So, the allowed transitions are :
J 0 <-> 1 ; 2 <-> 3 ; 4 <-> 5... as the odd(1,3,5..) states will not be populated(hence contradicting his own statement)... and no transitions as J 1 -> 2 ; 3 -> 4 ...

I raised the question in the class but he seemed a bit more confused after my question.

Can anyone confirm the authentication of his statements. And Please tell me what is right and what is wrong. Thanx.

...I checked everything on the internet (starting with wiki), and then asked the question here...by the way i got the answer...thanks for showing concern...

## 1. What is pure rotational spectra?

Pure rotational spectra refers to the study of the energy levels and transitions of a molecule as it rotates in its own axis. This type of spectra is characteristic of diatomic molecules like CO2.

## 2. What are the allowed transitions in pure rotational spectra?

The allowed transitions in pure rotational spectra are those between energy levels that have a difference in quantum number J of ±1. This is known as the selection rule for pure rotational spectra.

## 3. What is the significance of the allowed transitions in CO2 molecule?

The allowed transitions in CO2 molecule are of great significance as they provide information about the molecular structure and properties of CO2. By studying these transitions, we can determine the bond length and bond angle of the molecule, as well as its rotational constants.

## 4. How can the allowed transitions in pure rotational spectra be observed?

The allowed transitions in pure rotational spectra can be observed using spectroscopic techniques such as microwave spectroscopy or infrared spectroscopy. These techniques involve passing a beam of electromagnetic radiation through a sample of CO2 and analyzing the absorption or emission of specific wavelengths.

## 5. What factors affect the allowed transitions in pure rotational spectra?

The allowed transitions in pure rotational spectra are affected by several factors, including the moment of inertia of the molecule, its rotational constants, and the energy difference between the energy levels. These factors can be altered by changes in temperature, pressure, or the presence of other molecules in the sample.

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