  We report on the frequency stabilization of a 739 nm Ti:sapphire laser to a
hyperfine component of the $^{127}I_{2}$ B(1)-X(11) P(70) transition using
acousto-optic modulation transfer spectroscopy (MTS). A frequency stability of
$3.83\times 10^{-11}$ around 13 s averaging time is achieved when the laser
frequency is stabilized. The observed hyperfine transition of the molecular
iodine is an ideal frequency reference for locking the lasers used in
experiments with trapped ytterbium ions, since its second harmonic frequency is
the $^{2}S_{\frac{1}{2}}-^{2}P_{\frac{1}{2}}$ transition of the ytterbium ion
at 369.5 nm. By investigating the line broadening effects due to the iodine
vapor pressure and laser power, the locking is optimized to the theoretical
signal to noise ratio (TSNR) of this iodine transition.
