Accurate determination of OsO4 absolute frequency grid at 28/29 THz

We have performed a set of 10(-12) level accuracy frequency measurements on 40 OsO4 transitions, which extend over the 1.2 THz optical range from the P(22) to the R(26) (CO2)-C-12-O-16 lines of the 10.4 mu m laser emission ba nd. The measurements were made by heterodyning two OsO4 saturated, absorpti on-stabilized, CO2 laser radiations, with that of centimetric and millimetr ic sources, phase locked to a H-maser/Cs-clock, These measurements have bee n referenced against two OsO4 transitions known with 7 x 10(-13) uncertaint y.