# Quantum Chemistry/Example 20

An electronic transition of H atom from an energy level to the ground state is observed with a corresponding wavelength of 102.5 nm. Determine the initial state of the electron from which transition has occurred.

The Rydberg's phenomenological equation will be used to solve the energy transition problem

**Rydberg's phenomenological equation for hydrogen**

where the is Rydberg constant for hydrogen and is equal to 109737 . is the final energy level, is the initial energy level for hydrogen transition. Both and are integers and .

The wavelength is given as 103nm

Concert to SI units:

The H atom's transition is from unknown energy level to the ground state.

So we can know the final state is the ground state which means

The now can be calculated:

Because the energy level always

Therefore, the initial state of the electron from which transition has occurred is energy level 3.