Get vibration frequency form absorption spectra line

[want2graduate]

Homework Statement

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"Absorption spectra of gaeous HCl show a line at 3.5 μm which results form molecular vibration (oscillation from interatomic distance)" How do I get the frequency of vibration from this?

Homework Equations

? If I knew this, then I could probably solve the problem

The Attempt at a Solution

Is the wavelength 3.5μm? I don't see a relevant explanation in my book (An Introduction to Thermal Physics).

 

[phyzguy]

Yes, the fact that the absorption line is at 3.5 μm means that the wavelength of the absorbed radiation is 3.5 μm. The question asks what frequency is this radiation.

 

[want2graduate]

OK, thanks.

Also, I'm unsure about the last part of this question - to approximately what temperature would the gas have to be heated to excite vibrations thermally? Again, I feel like there is just some equation or basic fact that I should know to solve this, but it isn't clear to me what that would be.