0
$\begingroup$

In the spectrum of the blue part in a candle flame, there’s a violet emission at 432 nm due to excited CH* molecules (chemiluminescence). Why 432? Why not 400 or 500? There are emissions at 436, 475 and 520 nm too. Why these numbers? Is it because the energies of the photons emitted correspond to these wavelengths, as E = hc/λ?

$\endgroup$
0
$\begingroup$

Yes. And because those energies correspond to differences in energy between bonds in CH and C2 and bonds in the CO2 and H2O reaction products.

$\endgroup$
2
  • $\begingroup$ The wavelength of chemiluminescence is only related to energy difference between the electronically excited and the ground state of CH radical, not to the energy of other molecules and not really to bond energy. $\endgroup$
    – gigacyan
    Mar 17 '15 at 8:45
  • $\begingroup$ Very true. I should have taken more time with this. $\endgroup$
    – mmesser314
    Mar 17 '15 at 13:12
0
$\begingroup$

Atoms and small molecules have discrete energetic states. When an excited molecule relaxes to the ground state by emitting a photon, the energy (wavelength) of this photon is equal to the energy difference between the 2 states.

$\endgroup$
3
  • $\begingroup$ Is the photon’s energy unequal to the energy difference between the states? $\endgroup$
    – Michael Dy
    Mar 20 '15 at 6:40
  • $\begingroup$ It is equal to a energy difference between two states (of the same molecule). Since small molecules have not too many states, there is only a fixed number of wavelengths they can emit at. $\endgroup$
    – gigacyan
    Mar 20 '15 at 10:02
  • $\begingroup$ Your answer here is the answer to my other question too. If you want, copy your answer and paste it to that page. I’d make it the “accepted answer.” $\endgroup$
    – Michael Dy
    Mar 20 '15 at 13:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.