Infrared — Far Infrared Spectroscopy of Methanol by Optically Pumped Far Infrared Laser Emission

The classical techniques for studying the vibration-rotation spectra of molecules are broadband, based either on monochromators or on the Fourier transform principle. Their advantage is that the entire spectral region of interest can be covered, and the general view obtained in this way greatly facilitates the interpretation of a spectrum. Their main disadvantage is that they offer a resolution which is rarely better than 1 GHz, while the Doppler width is typically about 100 MHz. Even for fairly simple molecules there are often spectral regions where the density of lines is very high, and where there are no recognizable patterns. In such cases, a conventional unresolved spectrum will provide only rudimentary insight into the molecular vibration-rotation states.