Hyperfine Structure of the 47R(9-2), 48P(11-3) and 48R(15-5) Lines of127I2at 612 nm as Secondary Standards of Optical Frequency

A spectroscopic study of the 47R(9-2), 48P(11-3) and 48R(15-5) lines of the B-X electronic transition 127 I 2 iodine molecule at 612 nm was undertaken using a continuous-wave tunable dye laser. The uncertainty in the frequency interval measurements between the hyperfine components, of a few kHz, allows determination of the differences between constants of the four principal hyperfine interactions.