Vibrational /rotational temperature?

[hymeme]

I learned that Raman scattering can measure the vibrational / rotational temperature of certain species in a reacting flow. But couldn't figure out the physical meansing of these temperature. Why do we need such things? Can anyone help me? Thank you!

 

[jfizzix]

Temperature is the rate at which energy changes with respect to entropy, at constant volume, and particle number.

If you can have a system with different degrees of freedom what don't interact with one another, then each degree of freedom can be treated as an independent thermodynamic system, with its own energy, entropy, and temperature.

As an example, it is possible for the spins of atoms in a crystal to have independent (and sometimes even negative) temperatures from the vibrational degrees of freedom of the atom.

 

[hymeme]

Thank jfizzix for the reply! It helped some.
From some tables, we know that the rotational temperature of H2 is 88K. What does that imply? (Does it mean that to get the rotational bands, the temperature should be higher than 88K.) If H2 is at room temperature, or if it is at 1500K, will the rotational bands be significantly different? This is the area I am not familiar with.

 

[jfizzix]

Ah, the characteristic rotational temperature (the thing looked up in tables) is the temperature at which thermodynamic energy fluctuations (kbT) are on par with the transitions in the rotational part of the energy spectrum.

If you are above 88K, then the thermal fluctuations are on par with the rotational energy levels, so beyond that temperature, you probably need to consider more than just the translational degree of freedom in calculating things like the partition function, entropy, heat capacity, etc.

 

[sardar]

Vibrational and rotational temperature refer to the energy levels of molecules in a reacting flow. In simple terms, these temperatures represent the amount of energy that is being transferred and exchanged between the molecules through their vibrational and rotational motions. This information is important because it can give us insights into the chemical reactions taking place in the flow.

Raman scattering, a technique used to study the interaction of light with matter, allows us to measure these temperatures by analyzing the scattered light from the molecules. By understanding the vibrational and rotational temperatures, we can better understand the energy transfer and chemical reactions happening in the flow.

Knowing these temperatures can also help us optimize and control chemical reactions in various industrial processes, such as combustion engines and chemical reactors. It can also aid in the development of more efficient and environmentally friendly technologies.

In summary, vibrational and rotational temperature measurements are essential in understanding and controlling chemical reactions in a reacting flow, leading to advancements in various industries and technologies. I hope this helps clarify the concept for you.