MESOSPHERIC OBSERVATIONS AND MODELING OF THE ZEEMAN SPLIT 233.9 GHZ (OO)-O-18-O-16 LINE

Observations made from Kitt Peak, AZ, of the 233.9 GHz emission line o f (OO)-O-18-O-16 in the upper stratosphere and lower mesosphere are re ported. A good model fit to the line is obtained by incorporation of p ressure and temperature broadening effects, as well as a Zeeman splitt ing algorithm that uses a standard geomagnetic field model and a param agnetic Hamiltonian description of the molecular energy states. These observations are used, along with the well known (OO)-O-18-O-16 mixing ratio, to establish absolute calibration for observations of other ch emical species from Kitt Peak. Repeated measurements show no change in this absolute calibration between observation dates. The wide magneti c splitting (+/-1.8 MHz) exhibited by this line with only six Zeeman c omponents provides a unique test of middle atmosphere Zeeman effect mo del calculations, supporting the use of O-2 lines by microwave atmosph eric sounders to measure pressure and temperature.