Knowledge Bank

New heterodyne frequency measurements have been made on OCS absorption lines between 1860 and $1915cm-1$. Transitions from the ground state and from low lying vibrational states have been measured. By combining certain heterodyne measurements of hot bands with earlier heterodyne measurements, we obtain accurate calibration data in the 2700 to $3000cm-1$ region. The present heterodyne measurements use a CO laser as a local oscillator (or intermediate frequency standard) and a tunable diode laser locked to the peak of the OCS absorption line. The frequency of the local oscillator is measured against well known $CO2$ laser transitions at the same time that the CO-OCS frequency difference is measured. A summary of frequency calibration data available for OCS and $N2O$ will be presented. The heterodyne measurements will be compared with some recent FTS measurements from other laboratories as well as from our own laboratory.