  The SDSS-III APOGEE collaboration has identified a single useable line in the
H-band spectra of APOGEE target stars arising from a singly ionized species.
This line of Ti II (${\lambda}_{air}$ = 15873.84 {\AA}) is therefore of great
importance for use in stellar surface gravity, or log(g), determinations via
the Saha equation. While a theoretical estimate of the line strength exists, to
date no laboratory measurement of the line strength has been reported. Herein
we report an absolute laboratory transition probability measurement for this
important Ti II line. A relative line strength measurement is made of the Ti II
H-band line of interest and a reference line with a previously reported
absolute transition probability. This ratio is measured using multiple spectra
of a high-current water-cooled HC lamp recorded with a calibrated FT-IR
spectrometer.
