vibrotspec

vibrotspec - Vibrational-Rotational Spectroscopy...

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Vibrational-Rotational Spectroscopy Vibrational-Rotational Spectrum of Heteronuclear Diatomic Absorption of mid-infrared light (~300-4000 cm -1 ): Molecules can change vibrational and rotational states Typically at room temperature, only ground vibrational state populated but several rotational levels may be populated. Treating as harmonic oscillator and rigid rotor: subject to selection rules Δ v = ± 1 and Δ J = ± 1 E field E vib + Δ E rot = ω = E f E i = E ( v , J ) − E ( v ′′ , J ) v = = ⎡ v 0 ( v ′+ 1 2 ) + BJ ( J 1 ) − ⎡ v 0 ( v + 1 2 ) + BJ ( J ′′+ 1 ) 2 π c At room temperature, typically v=0 and Δ v = +1: =+ 1 ( vv 0 B J ( J ) J J ′′+ 1 ) Now, since higher lying rotational levels can be populated, we can have: J 1 = J + 1 = + 2 ( + ) J 1 J = J 1 0 2 BJ P Δ= + J 0 B J 1 R branch = branch
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By measuring absorption splittings, we can get B . From that, the bond length! In polyatomics, we can also have a Q branch, where Δ J0 and all transitions lie at = ν = ν 0 . This transition is allowed for perpendicular bands:
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This note was uploaded on 11/27/2011 for the course CHEM 5.43 taught by Professor Timothyf.jamison during the Spring '07 term at MIT.

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vibrotspec - Vibrational-Rotational Spectroscopy...

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