The Excited atom is ultimately to return to the ground state and then emission spectra, but the way to return to the ground state can be varied, So there are many spectral line with various wavelength in the emission spectra.
If an atom is excited to the energy level, the transitions between energy levels have different possibilities; it can be I1, Im, IO, LM, and mo. Of course， according to quantum mechanics，some transitions between energy levels are not allowed. But the transition allowed produces a wavelength of spectral line.
The Spectral line intensity is determined by the vapor cloud ，in this element ，many atoms are excited and produces the same transition, the im which is any transition determined the intensity of spectral lines (of the total intensity).
In the Formula:
Ni is excited to the energy level I of the atomic concentration.
Aim is the transition probability between I level and m level.
Hvim is the energy that Ei minus Em.
VIM is the frequency of emissing spectral line.
It can have the conclusion and discussion:
1. The higher the excitation potential to be excited to the energy level, the lower the atom concentration is in this state.
2. From different high energy level transition to the ground state, the higher of level, and the smaller probability of the transition.
3. The minimum excitation energy of elements and atoms to be excited is resonance potential. The energy level transition to the ground state emission spectral line called resonance line. Due to the strong concentration of being excited to this state atomic, the transition probability is also big; the resonance line is the strongest line and the most sensitive line.
4 . The spectral lines launched when the same high energy level transit to a different energy level as identical, even if the light source fluctuated, and the relative strength Can be maintained. This line can be used in quantitative analysis.
5. Considered of the ionization and excitation, the relationships between spectral line intensity and temperature general represented as followed curve figure. Curves show that the spectral line intensity is not larger when the temperature higher, but each one has its most suitable temperature. At this temperature, the spectral line is strongest.
6. The photoelectric spectral analysis is a relative method, excited the knowing content of standard samples and analysis of samples together, comparison line is also used in photoelectric spectral analysis, it is use the relative intensity to analysis the elements of the samples.