microwave spectroscopy

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June 30, 2026

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Microwave spectroscopy is a technique used to study the rotational transitions of molecules. These transitions occur when a molecule absorbs microwave radiation, causing it to move from a lower rotational energy state to a higher one. The microwave region of the electromagnetic spectrum spans frequencies from 1 to 1,000 gigahertz.1

This method is valuable for determining precise molecular structures, including bond lengths and angles, as well as other properties like electric dipole moments. It requires molecules to have a permanent electric dipole moment and be in a gaseous state at very low pressures. Microwave spectroscopy has been instrumental in identifying molecules in outer space and has led to the detailed structural analysis of thousands of molecules.21

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spectroscopy
Microwave spectroscopy
For diatomic molecules the rotational constants for all but the very lightest ones lie in the range of 1–200 gigahertz (GH_z). The frequency of a rotational transition is given approximately by ν = 2B(J + 1), and so molecular rotational spectra will exhibit…
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For diatomic molecules the rotational constants for all but the very lightest ones lie in the range of 1–200 gigahertz (GH_z). The frequency of a rotational transition is given approximately by ν = 2B(J + 1), and so molecular rotational spectra will exhibit…
Read More

Venus
Observations from Earth
Observations in the microwave portion of the spectrum, beginning in earnest in the late 1950s and early ’60s, provided the first evidence of the extremely high surface temperatures on the planet and prompted the study of the greenhouse effect as a means of producing these temperatures.
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Observations in the microwave portion of the spectrum, beginning in earnest in the late 1950s and early ’60s, provided the first evidence of the extremely high surface temperatures on the planet and prompted the study of the greenhouse effect as a means of producing these temperatures.
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spectroscopy
Origins
…as radio-frequency (rf) spectra, or microwave spectra; they are observed typically in the frequency range from 10⁶ to 10¹¹ hertz.
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…as radio-frequency (rf) spectra, or microwave spectra; they are observed typically in the frequency range from 10⁶ to 10¹¹ hertz.
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spectroscopy
Microwave spectroscopy was used to discover the so-called three-degree blackbody radiation, the remnant of the big bang (i.e., the primeval explosion) from which the universe is thought to have originated (see below Survey of optical spectroscopy: General
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Microwave spectroscopy was used to discover the so-called three-degree blackbody radiation, the remnant of the big bang (i.e., the primeval explosion) from which the universe is thought to have originated (see below Survey of optical spectroscopy: General
Read More