MEASUREMENT OF ABSOLUTE INTENSITIES IN MICROWAVE ROTATIONAL SPECTROSCOPY

This work was supported in part by National Science Foundation Grant GP 6305X.Author Institution: Hewlett-Packard Company Palo Alto; Chemistry Department, Rice UniversityA method of calibrating signal strength for the Hewlett-Packard spectrometer by introducing a known modulation index has been devised. The curve of power versus grid voltage for the frequency stabilized backward wave oscillator microwave source is determined. Then a small, known 33.3 kHz square wave voltage is applied to the grid. From the magnitude of this voltage and the power versus grid voltage curve, the modulation index may be calculated and the propertionality constant (overall gain constant) relating signal strength to modulation index determined. The absolute intensities of the lines of several compounds have been measured and compared with theory. Both the maximum peak signal ($\eta$) method and the product of unsaturated absorption coefficient and unsaturated line width ($\gamma_{0} \Delta$) method have been used and will be compared. Application of absolute intensity measurement to quantitative analysis and to determination of thermodynamic quantities will be discussed