1. The problem statement, all variables and given/known data I figured out 4a, but I'm just struggling a bit with 4b. 2. Relevant equations Relevant websites highlighted above (respectively): http://www.nist.gov/pml/data/handbook/index2.cfm http://physics.nist.gov/PhysRefData/ASD/lines_form.html 3. The attempt at a solution This is regarding question 4b. While I was able to figure out that ni = 4 and nf = 2, my professor is looking for the specific states (e.g. 4d->2p). I went to his office hours and talked to him, but he didn't really want to point out more than the usual Hydrogen energy level diagrams like found here (I think he was afraid of giving it away. His only hint was that there are "a few"): http://astro.unl.edu/naap/hydrogen/transitions.html The course is actually a laser class, so unfortunately our textbook does not cover this (we won't use it until later in the year), and none of my old chemistry or quantum notes really help with identifying this. I also did a lot of searching and could never really find anything that talks about this. I also tried using the NIST website and wrote down 5 by looking up H levels between 485 and 487 nm, but he said that was too many. I read somewhere mention that 4d->2p is a valid state, but I could not find any material to back up the claim or how that conclusion was come to. Where would I get started with this problem? Thanks a bunch!