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Summary form only given. We present a dense grid of high precision reference lines in the hyperfine structure of the B-X system of I/sub 2/. With the use of an actively stabilized etalon, locked to the output of a He-Ne laser, which is itself locked to a /sup 129/I/sub 2/ hyperfine resonance, we have measured the absolute frequency of hyperfine components of nearly 600 lines in the range 571-655 nm; the precision obtained by interpolation methods is 1 MHz. From a calculation of the hyperfine structure centres-of-gravity of the rotational structure were determined, which were incorporated in fits to the rotational structure of 21 bands in the B-X system. With the 21 bands investigated predictions of 6000 t-hyperfine components in the range 571-655 nm were calculated with a reference line in each interval of 1 cm/sup -1/. Since continuous wave single-mode lasers usually can be scanned over intervals of 1 cm/sup -1/ this grid of lines provides a useful secondary frequency standard in many laser spectroscopic investigations requiring accuracies of 1 MHz.