Photoexcitation rates for creation of ultralong-range Rydberg molecules (ULRM) with 31$lesssim n lesssim41$ in both ground and excited vibrational levels in cold ($Tsim900$~nK) gases of polarized and unpolarized $^{87}$Sr are presented. The measured production rates of the $ u=0, 1$ and 2 vibrational levels reveal rather different $n$ dependences which are analyzed by evaluating the Franck-Condon factors associated with excitation of the different vibrational levels and molecular rotational states. In particular, for gases of spin-polarized fermions, only Rydberg dimers with odd rotational quantum numbers are excited due to the requirement that their wavefunctions be anti-symmetric with respect to exchange. The data also demonstrate that measurements of the formation of vibrationally-excited $ u=1$ molecules can furnish a probe of pair correlations over intermediate length scales extending from $sim20$~nm to greater than 250~nm.
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