emily asked in 科學及數學化學 · 1 decade ago

急ar!!plz About the IR calculation frequency and wavenumber

Calculate approximate frequency and wavenumber of the C-H stretching

vibration knowing that the force constant of C-H bond k = 500 N m-1. To

which part of the electromagnetic spectrum would this frequency belong?

Note that carbon atom is much heavier than hydrogen atom.

v= 1/2π √(k/m eff)

(h = 6.626 x 10-34 J s; c = 2.998 x 108 m s-1; NA = 6.022 x 1023 mol-1)

Thank you very much

1 Answer

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  • 1 decade ago
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    Since the carbon atom is much heavier than hydrogen atom, meff can be approximated as the mass of a single H atom = 1.66 x 10-27 kg.

    Hence v = (1/2π) √(500/1.66 x 10-27) = 8.733 x 1013 Hz

    And the wavelength is:

    c/v = 2.998 x 108/8.733 x 1013

    = 3.433 x 10-6 m or 3.433 x 10-4 cm

    Finally the wavenumber is 1/3.433 x 10-4 = 2913 cm-1.

    Source(s): My chemical knowledge
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