Vacuum ultraviolet 6-m monochromator.

A description is given of the design and construction of the Adelaide 6.65-m VUV monochromator. The instrument has an off-plane Eagle mounting and can be used in the first order over a wavelength range from central image to 460 nm. Digital encoders are used to monitor the angular rotation and linear displacement of the grating to provide servocontrolled wavelength and focusing adjustments which are electronically (rather than mechanically) coupled and operated through a programmable calculator. The monochromator is designed for high resolution studies of photoabsorption in atmospheric gases, and its performance is illustrated by reference to absorption studies in portions of the Schumann-Runge band system of molecular oxygen.