There are various absorption lines that correspond to the difference in energy levels between electron orbits. E.g. the https://en.wikipedia.org/wiki/Lyman-alpha_line correpsonding to the difference in energy between an electron orbiting a hydrogen atom in its ground state and the $n=2$ orbital.
But how "wide" are these lines? How large is the range of values that can cause a hydrogen atom to absorb these photons and excite the electron. And what happens to the energy above the bare minimum required?
Similarly, how wide are the emission lines?
Best Answer
There are basically 3 broadening mechanisms for spectral lines
natural broadening due the finite lifetime of atomic states (states that decay faster lead to broader lines),
Doppler broadening due to the thermal velocities of the atoms,
pressure/collisional broadening due to collisions of the radiating atom with other particles (whilst these collisions may not actually shorten the lifetime of the level, they introduce random phase jumps of the emitted wave, which have the same effect on the observed line width).
For more see http://www-star.st-and.ac.uk/~kw25/teaching/nebulae/lecture08_linewidths.pdf