Heterodyne measurements of 12C16O laser frequencies and improved Dunham coefficients

Earlier measurements of absolute frequencies of 12C16O laser lines by heterodyning with second harmonics of a 12C16O2 laser have been extended to 15 more lines by use of the rare isotopes 12C18O2 and 13C16O2. Interband difference frequencies for 20 pairs of 12C16O lines have also been measured by beat frequency techniques. These data together with 1438 other previously reported frequency measurements in the microwave and infrared regions have been analyzed to determine coefficients of a Dunham series E vJ = Σ m,n Y mn (v + 1 2 ) m [J(J + 1)] n for the CO electronic ground state. Transition frequencies predicted from the derived coefficients are substantially more accurate than earlier tabulations, having estimated uncertainties of the order of 2 MHz in the strongest laser bands. The coefficient Y31 has been determined for the first time.