Find units of transition dipole moment

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SUMMARY

The correct formula for the relationship between oscillator strength (f) and transition dipole moment (μ²) is given by f = [(2*π*m*e)/(3*h*ε₀)] * νₐᵣ * μ²ᵍᵉ. Here, m represents the mass of an electron, e is the charge of an electron, h is Planck's constant, ε₀ is the permittivity of free space, and νₐᵣ is the mean absorption frequency in cm⁻¹. The discussion highlights confusion regarding the constants and units involved in calculating oscillator strength, particularly the distinction between frequency and wavenumber. Accurate calculations require careful attention to these units to ensure dimensionless results.

PREREQUISITES
  • Understanding of quantum mechanics principles, particularly related to transition dipole moments.
  • Familiarity with the concepts of oscillator strength and its significance in spectroscopy.
  • Knowledge of fundamental constants such as Planck's constant (h), mass of an electron (m), and charge of an electron (e).
  • Ability to perform unit conversions between frequency and wavenumber.
NEXT STEPS
  • Research the derivation of the oscillator strength formula in quantum mechanics.
  • Learn about the significance of transition dipole moments in molecular spectroscopy.
  • Explore the implications of using different units (frequency vs. wavenumber) in calculations.
  • Investigate common pitfalls in calculating oscillator strength and transition dipole moments.
USEFUL FOR

Researchers in quantum chemistry, physicists studying molecular transitions, and anyone involved in spectroscopy and related calculations will benefit from this discussion.

sshrestha
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I have been trying to figure out which formula for the relationship between oscillator strength and transition dipole moment is correct.

Wiki had the following formula:

http://photonicswiki.org/index.php?title=Transition_Dipole_Moment

f = 4.703 \times 10^{29} \bar{v} \mu^{2}_{ge}\,\!

where

\bar{v}\,\! is the mean absorption frequency of the band in cm–1

\mu^{2}_{ge}\,\!, refers to the square of the transition dipole moment between the ground state and the excited state.

What I am unsure about is how they got the value of the constants and the units for it.

In another reference I had this formula:

f =[(8*pi*massofelectron)/(3*planck's const*electric)charge^2)] *vbar*u^2

When I calculate the constant using this formula I get 4.49 * 10^41. Moreover I am also confused about whether vbar is frequency or wavenumber. Since wavenumber is in cm^-1 the units don't cancel out and f is no longer dimensionless. Has anyone done this kind of calculation?

The values that I have in order to calculate the transition dipole moment is energy and f.

I use E = Planck's const*frequency to get frequency and then c= frequency*wavelenth to get the wave number and plug it in the equation. In either case the value I get is very off. Can you please help me figure out where I am missing the point?
 
Physics news on Phys.org
The correct formula for the relationship between oscillator strength and transition dipole moment is:f = [ (2*π*m*e)/(3*h*ε₀) ] *νₐᵣ*μ²ᵍᵉwhere:f is the oscillator strength,m is the mass of an electron,e is the charge of an electron,h is Planck's constant,ε₀ is the permittivity of free space,νₐᵣ is the mean absorption frequency in cm⁻¹, andμ²ᵍᵉ is the square of the transition dipole moment.
 

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