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…

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.

…as radio-frequency (rf) spectra, or microwave spectra; they are observed typically in the frequency range from 10⁶ to 10¹¹ hertz.

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