Re: Excitation and Emission Spectrum


raconte@xxxxxxxxxxx wrote:
> Farooq W wrote:
> > The basic question is the the
> > absorption spectrum and the excitation spectrum are one and the same
> > thing for a luminescent molecule?
> >
> Not necessicarily. The wavelength of maximum absorbance is a good
> starting point for determining fluorescence excitation, but other
> wavelengths may be just as good. As an example again, anthracene's
> excitation max is not it's absorbance max.
>
> > Let us see this equation from a reference:
> > fluorescent intensity I (_f_) = 2.303( Phi_f)(Io)E bC
> >
> > where phi_f is flurorescence efficiency, Io Intensity of incident beam,
> > E is molar absorptivity, b and C are path length and concentration
> > respectively.
>
> Nice, ... but,
>
> >
> > Now if we assume that Phi-f is wavelength independent,
>
> Does your reference explicitly say this?
He makes an assumption of that.

>I don't have a good one
> before me, but this seems counterintuitive to me. Although it could be
> true. I'm just an analytical lab monkey, after all, not a freakin'
> quantum physical chemist.
>
> > then I(_f_), as
> > a
> > function of exciting wavelength would give a same shape as that of the
> > absortion spectrum...this is okay.
>
> > For this reason, the author writes,
> > absorption and excitation spectra are used interchangeably in
> > fluorescence spectroscopy; but it must be realized that the methods of
> > acquiring *normal* absorption spectrum and excitation spectrum are
> > fundamentally different! The para ends here with no further reference
> > the *fundamental* difference with no clue whatsoever, perhaps he is
> > referring to the different geometry used for measuring abs. and excit.
> > spectrum.
> >
> The statement is confusing, you're right. Does the author mean the
> case I cite above, or the geometry, or something else. You may have to
> take a trip to the local university and talk face to face with a
> physical chemist to get to the bottom of this.

I do go there everyday, but I don't feel there is a good physical
chemist with whom this can be discussed. Those who were, have left. The
same discussion is going on in CHEMED-l at
http://mailer.uwf.edu/listserv/wa.exe?A1=ind0508&L=chemed-l if you are
interested.

>You may simply been
> stymied by some bad terminology or jargon, or some fundamental of
> florescence has been glossed over in your reference.
>
> Best of luck.

.

Relevant Pages

  • Re: Excitation and Emission Spectrum
    ... > absorption spectrum and the excitation spectrum are one and the same ... Does your reference explicitly say this? ...
    (sci.chem)
  • Re: Spectrum!
    ... | Androcles wrote: ... |> its absorption lines with it, blatantly obviously it would it would ... |> become a spectral class G and be a cooler star, blatantly obviously, ... |> shows a class M spectrum, ...
    (sci.physics.relativity)
  • Re: Classical Blackbody Radiation Spectrum
    ... How does absorption result in equilibrium? ... you see a non-distorted source spectrum, say, f. ... radiation with the same temperature T as the BB. ...
    (sci.physics.research)
  • Re: Atomic hydrogen absorption spectra in far UV
    ... >>the absorption spectrum of H. On the other hand, ... that the problem with chemistry is that it's too difficult for chemists. ... engineer was oblivious to their existence. ...
    (sci.physics.research)
  • Re: More on Lorenz contraction
    ... It is, however, a correct animation of the absolute position of the ... lines to do, Wahrsager Tusselad, and these are unaffected by a Doppler ... | (In Algol, the two sets of absorption lines are different, ... Pity they in a spectrum too to don't. ...
    (sci.physics.relativity)