Abstract

A technique for recording high-resolution, broadly tunable absorption spectra in the ultraviolet (UV) and vacuum ultraviolet (VUV) is described. A supersonic expansion is used to prepare molecules in a rovibrationally cold distribution of states, and a dispersed broad-band deuterium (D2) lamp is used for excitation. The attenuation of light due to absorption is measured with the use of dual gate detection during pulsed valve-on and valve-off periods. The VUV light beam, after crossing the supersonic expansion, is frequency down-converted with a scintillator-coated exit window, and the resulting light intensity is measured by boxcar integration or photon counting. A simple sample delivery system and complete software control of the experiment make this system a routine laboratory spectrometer. Sensitivity and resolution are discussed, and the device is demonstrated for the molecules NH3 and CH3I.

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