Molecular physics
Molecular physics is the study of the physical properties of molecules and molecular dynamics. The field overlaps significantly with physical chemistry, chemical physics, and quantum chemistry. It is often considered as a sub-field of atomic, molecular, and optical physics. Research groups studying molecular physics are typically designated as one of these other fields. Molecular physics addresses phenomena due to both molecular structure and individual atomic processes within molecules. Like atomic physics, it relies on a combination of classical and quantum mechanics to describe interactions between electromagnetic radiation and matter. Experiments in the field often rely heavily on techniques borrowed from atomic physics, such as spectroscopy and scattering.
Molecular structure
In a molecule, both the
Molecular energy levels and spectra
When atoms join into molecules, their inner electrons remain bound to their original nucleus while the outer
In addition to the electronic energy levels shared with atoms, molecules have additional quantized energy levels corresponding to vibrational and rotational states. Vibrational energy levels refer to motion of the nuclei about their equilibrium positions in the molecule. The approximate energy spacing of these levels can be estimated by treating each nucleus as a quantum harmonic oscillator in the potential produced by the molecule, and comparing its associated frequency to that of an electron experiencing the same potential. The result is an energy spacing about 100× smaller than that for electronic levels. In agreement with this estimate, vibrational spectra show transitions in the near infrared (about 1–5 μm).[2] Finally, rotational energy states describe semi-rigid rotation of the entire molecule and produce transition wavelengths in the far infrared and microwave regions (about 100-10,000 μm in wavelength). These are the smallest energy spacings, and their size can be understood by comparing the energy of a diatomic molecule with internuclear spacing ~ 1 Å to the energy of a valence electron (estimated above as ~ ħ/a).[1]
Actual molecular spectra also show transitions which simultaneously couple electronic, vibrational, and rotational states. For example, transitions involving both rotational and vibrational states are often referred to as rotational-vibrational or rovibrational transitions. Vibronic transitions combine electronic and vibrational transitions, and rovibronic transitions combine electronic, rotational, and vibrational transitions. Due to the very different frequencies associated with each type of transition, the wavelengths associated with these mixed transitions vary across the electromagnetic spectrum.[2]
Experiments
In general, the goals of molecular physics experiments are to characterize shape and size, electric and magnetic properties, internal energy levels, and
Current research
Within atomic, molecular, and optical physics, there are numerous studies using molecules to verify fundamental constants and probe for
See also
- Born–Oppenheimer approximation
- Electrostatic deflection (molecular physics/nanotechnology)
- Molecular energy state
- Molecular modeling
- Rigid rotor
- Spectroscopy
- Physical chemistry
- Chemical Physics
- Quantum Chemistry
Sources
- ATOMIC, MOLECULAR AND OPTICAL PHYSICS: NEW RESEARCH by L.T. Chen; Nova Science Publishers, Inc. New York
References
- ^ ISBN 0-470-20424-9.
- ^ .
- S2CID 40747565.
- S2CID 33254969.
- S2CID 115982983.
- .