But when an atom
absorbs a photon that has precisely the same energy needed by the
electron in a lower energy state to make transitions to a higher energy
state, the process is called absorption Thus if photons with a continuous
range of frequencies pass through a rarefied gas and then are analysed
with a spectrometer, a series of dark spectral absorption lines appear in
the continuous spectrum The dark lines indicate the frequencies that
have been absorbed by the atoms of the gas The explanation of the hydrogen atom spectrum provided by Bohr’s
model was a brilliant achievement, which greatly stimulated progress
towards the modern quantum theory