A Broadband Submillimeter Wave Spectrometer System with On‐Line Microcomputer Data Analysis

A submillimeter wave spectrometer operating in the frequency range 100 to 800 GHz has been constructed for the study of transient molecules in the gas phase. The instrument employs harmonic generation of millimeter wave frequencies and a He‐cooled InSb photoconducting detector. A high degree of flexibility is achieved using an exchangeable free‐space Pyrex absorption cell and a microcomputer for on‐line data analysis. The spectrometer can be operated in a free‐running video mode together with a fast signal averager or phase‐locked to a microwave reference with source modulation. It is shown that the reproducibility of line center frequency measurements up to 600 GHz is ± 10 kHz. Transitions with absorption coefficients of at least 3 · 10−8 cm−1 can be detected in the range from 150 to 250 GHz. Ground state rotational transitions of OCS between 200 and 690 GHz are reported and analysed together with previous data.