Rotational–vibrational spectroscopy

Rotational–vibrational spectroscopy studies molecular absorption or emission involving simultaneous changes in rotational and vibrational energy states, usually in the infrared.

Molecular vibration: Periodic motion of atoms about their equilibrium positions in a molecule. Vibrational transitions provide the energy change around which rotational lines are organized.
Quantum mechanics: The physical theory describing matter and radiation at atomic and subatomic scales. Quantized molecular states underpin the discrete transitions measured in rovibrational spectra.
Fourier-transform infrared spectroscopy: An infrared measurement method that derives a spectrum from an interferogram using a Fourier transform. It records dense rovibrational spectra efficiently across broad infrared ranges.
Pure rotational spectroscopy: The study of molecular transitions that change rotational energy without changing vibrational state. It isolates rotational transitions rather than the combined changes that define rovibrational bands.
Hydrogen chloride: A diatomic molecule composed of one hydrogen atom and one chlorine atom. Its infrared-active vibration produces a clear rotationally resolved band.
Molecular rotation: The rotational motion of a molecule, described by quantized angular momentum states. Changes between rotational states split vibrational bands into multiple spectral lines.
Dipole moment: A vector measure of the separation of positive and negative charge in a system. An oscillating dipole moment allows a molecular vibration to absorb infrared radiation.
Atmospheric spectroscopy: The study of atmospheric composition and conditions through interactions between radiation and atmospheric matter. Atmospheric gases are identified and quantified through their rovibrational absorption lines.
Vibrational spectroscopy: The study of transitions between molecular vibrational energy states. It often treats vibrational bands without resolving their rotational fine structure.
Carbon monoxide: A diatomic molecule consisting of one carbon atom bonded to one oxygen atom. Its simple rovibrational spectrum is a standard test of diatomic molecular models.

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Rotational spectroscopyRelated: Its bands combine rotational fine structure with vibrational energy changes.