Precise frequency measurements of ¹²⁷I₂ lines in the wavelength region 750-780 nm

High precision frequency measurements of ¹²⁷I₂ hyperfine transitions in the wavelength range between 750 and 780 nm were performed employing an optical frequency comb. A Ti:sapphire laser is frequency stabilized to a hyperfine component of I₂ using a Doppler-free frequency modulation technique, and an optical frequency comb is used to measure its frequency precisely. Improved absolute frequencies of 27 hyperfine transitions between 750 and 780 nm of the bands (0-12) and (0-13) of B ³π₀u + -X ¹σ⁺_g system of I₂ are presented. The relative uncertainty of the measurement is a few times 10?10, limited by the frequency instability of the iodinestabilized laser. The frequencies are compared to the predicted frequencies using the model description of [Eur. Phys. J. D 28, 199 (2004)], which yields differences larger than expected. An improved model is developed for the range from 755 to 815 nm for the prediction of lines with an error limit of the absolute frequency less than 0.2 MHz.