KARNATAKA SET 2024
A metastable ion has:
Correct Answer: (D) Higher potential energy than normal ions
A metastable ion is an excited ion that possesses excess internal energy to fragment into a smaller ion and a neutral fragment after it has been accelerated out of the ion source but before it reaches the detector. In the context of molecular physics and mass spectrometry:
- Internal Energy as Potential: The excess energy required for the ion to eventually fragment is stored as internal potential energy within its chemical bonds and electronic states.
- Instability: Because they have higher potential energy than "normal" stable ions, they exist in a state of precarious equilibrium and will likely decompose into a daughter ion and a neutral fragment during flight.
- Kinetic Energy: In a mass spectrometer, kinetic energy is determined by the acceleration voltage (eV). Both normal and metastable ions are accelerated by the same potential, so their initial kinetic energy is generally the same.
Comparison of Normal vs. Metastable Ions
| Ion Type | Stability | Energy State | Behavior |
|---|---|---|---|
| Normal Ion | Stable | Low Potential Energy | Reaches detector intact. |
| Metastable Ion | Unstable | High Potential Energy | Fragments during flight. |