Absorption and emission spectroscopy of atoms

[MartinG]

Hello !

As I understand it, the different isotopes of the same atom have a slightly different spectroscopic absorption and emission where, for example, Deuterium absorbs slightly shorter wavelengths than Protium.

My question is if two isotopes of different atoms, for example Tritium and Helium 3, which have three nucleons in both atoms, the spectroscopic absorption and emission of the different Isotopes is the same or different?

I thank you in advance for your responses.

 

[hutchphd]

The primary interaction in an atom is Coulombic. The effects of the mass of the heavier nucleus is predominately to alter the "reduced mass" $$\mu=m_e\frac 1 {1+\frac {m_e} {m_{nucleus}}}$$This is small and easy.
The other effects, which change nucleic charge (and electron number), affect all aspects of the interaction and produce major changes to the calculation and its outcome

 

[Twigg]

My question is if two isotopes of different atoms, for example Tritium and Helium 3, which have three nucleons in both atoms, the spectroscopic absorption and emission of the different Isotopes is the same or different?

Very different.

Changing the number of protons and/or electrons in an atom will change it's coarse structure (at the level where even the Bohr model can predict a change). These changes are of order 0.1 - 1eV. Changing the number of neutrons in the nucleus changes the atom's spectrum at the hyperfine level (caused by magnetic interactions between the nuclear spin and the electrons' orbit and spin). These changes are at the level of 0.00001 - 0.0001 eV.

 

[mfb]

Helium nuclei have twice the charge, which scales all energy levels with a factor 4. Instead of -13.6 eV the lowest energy state is now at about -54 eV. That's far more important than the relatively small isotope effect.