Observed intensity of Persistent Lines of Neutral Hydrogen

[edguy99]

The site http://physics.nist.gov/PhysRefData/Handbook/Tables/hydrogentable3.htm shows the intensity of various photon energy values from hydrogen. I was not able to see how this intensity was observed (ie. was it from a specific experiment, or does one simply look at the sun and count photons at this energy?). The references, from what I could see, seem to deal more with calculation of levels rather then calculating observed intensity.

To make the long question short: Why is the 2p3/2 to 1s1/2 (1215.66824 angstroms) transition twice the intensity of the 2p1/2 to 1s1/2 (1215.67364 angstroms) transition? Is it because the 3/2 has 4 states and the 1/2 only 2 states and we assume all the states are equally populated?

Another question: Why is the 2p to 1s transitions 5 times more likely then the 3p to 1s transition? ... what is the general rule for understanding the intensity column?

 

[azntoon]

The intensity of the 2p3/2 to 1s1/2 transition is twice the intensity of the 2p1/2 to 1s1/2 transition because the former has four possible energy levels while the latter has only two. The general rule for understanding the intensity column is that the higher the number, the more likely it is that the transition will occur. For example, the 2p to 1s transitions are five times more likely than the 3p to 1s transitions because they involve more possible energy levels.