Frequency of the ultranarrow S0 1 - P2 3 transition in Sr 87

We determine the frequency of the ultranarrow $^{87}\\mathrm{Sr}\\phantom{\\rule{4pt}{0ex}}^{1}S_{0}\\ensuremath{-}^{3}P_{2}$ transition by spectroscopy of an ultracold gas. This transition is referenced to four molecular iodine lines that are observed by Doppler-free saturation spectroscopy of hot iodine vapor. The frequency differences between the Sr and the ${\\mathrm{I}}_{2}$ transitions are measured with an uncertainty of $0.5\\phantom{\\rule{0.28em}{0ex}}\\mathrm{MHz}$. The absolute frequency of the $^{87}\\mathrm{Sr}\\phantom{\\rule{4pt}{0ex}}^{1}S_{0}\\ensuremath{-}^{3}P_{2}$ (${\\text{F}}^{\\ensuremath{'}}=7/2$) transition is $446\\phantom{\\rule{0.16em}{0ex}}648\\phantom{\\rule{0.16em}{0ex}}775(30)\\phantom{\\rule{0.28em}{0ex}}\\mathrm{MHz}$ and limited in accuracy by the iodine reference. This work prepares the use of the Sr $^{1}S_{0}\\ensuremath{-}^{3}P_{2}$ transition for quantum simulation and computation.