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 $\text{E}{}_{\mathrm{vJ}}\text{=}\text{Σ}{}_{\mathrm{m,n}}\text{Y}{}_{\mathrm{mn}}\text{(v +}\text{1}\text{2}\text{)}{}^{\mathrm{m}}\text{J(J + 1)]}{}^{\mathrm{n}}$ 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.