Microwave rotational spectroscopy

The region of planetary atmospheres upward of 1 millimeter is considered. The applications of this region, how microwave, millimeter, and submillimeter spectra (the so called rotational spectra) can fruitfully interact with infrared spectral measurements are described. Both the rotational bands and vibrational bands of molecules are considered. A typical rotational absorption coefficient for a linear molecule in a low J state with a dipole moment of about one Debye is plotted and evaluated. A vibrational case was chosen similarly: the transition dipole moment used for the vibrational case is typical of CO at the peak of its rotational distribution. Information on high altitude parameters that often cannot be obtained from higher frequency spectra, which can be provided by rotational spectra is discussed.