Knowledge Bank

By combining the techniques of supersonic jet spectroscopy and Fourier transform infrared spectroscopy, a new method for obtaining the infrared absorption spectra of rotationally cooled gaseous molecules has been developed. With this method the entire high resolution spectrum is obtained over a wide frequency range e.g. 400 to $4000cm-1$ using a pure unskimmed jet. Study of the intensity distribution of the cooled ammonia spectrum, has yielded information about the collisional energy transfer during the expansion of the gas. A model for the cooling process, which is consistent with these data and with the collisional selection rules, has been formulated.