Quantised Energy Level
Definition
An allowed state of an atom or molecule. Transitions between levels happen only at discrete energies set by the level spacing, not at any arbitrary energy. The discreteness is what makes spectra characteristic rather than continuous.
- Definition
- Allowed discrete energy state of an atom or molecule
- Transitions
- Occur only at fixed energy spacings
- Consequence
- Produces characteristic, not continuous, spectra
- Field
- Atomic and molecular spectroscopy
Common questions
Why does the discreteness of energy levels make spectroscopy useful for forensic material identification?+
Because each element or compound has a unique set of allowed energy transitions, the wavelengths at which it absorbs or emits light form a distinctive pattern, much like a fingerprint, that analysts match against reference spectra to identify unknown substances.
How does temperature affect which quantised transitions are observed in a spectrum?+
Higher temperature populates higher-energy starting states more heavily, which can activate additional transitions or shift relative peak intensities, so spectroscopic techniques often control or record sample temperature to keep spectra comparable to reference conditions.
Related terms
- Band Spectrum
- A continuous-looking envelope of closely spaced lines produced by molecules. Electronic, vibrational and rotational transitions couple together so a single electronic excitation...
- Beer-Lambert Law
- A = εbc. Absorbance equals molar absorptivity times path length times concentration. The linear relation between absorbance and concentration that makes UV-Vis...
- Line Spectrum
- A discrete pattern of sharp lines produced by atoms in the gas phase. Each element has a unique line pattern set by...
- Selection Rule
- A quantum-mechanical rule that decides whether a transition between two levels is allowed or forbidden. Allowed transitions are intense and fast; forbidden...
- Wavenumber (Cm⁻¹)
- The number of wavelengths per centimetre, equal to 1/λ when λ is in cm. The working unit of vibrational spectroscopy because it...