This research investigates the infrared absorption intensity and isotope-dependent frequency shifts of CH stretching on diamond C(111) single-crystal surfaces by Fourier transform infrared spectroscopy (IRS). By employing single-pass direct absorption and in situ surface oxidation methods, a single sharp feature at nu(m)=2832.2+/-0.9 cm(-1) with a FWHM of Gamma approximate to 6 cm(-1) is observed at 800 K. Systematic measuring of how band intensity depends on hydrogen etching time indicates that a well hydrogen-terminated C(111)-1 X 1 can be prepared only after prolonged exposure of the surface to H, generated by hot W filaments, at 1100 K. A study of the band intensity at saturation, and assuming an electronic polarizability of alpha(e)=0.65 Angstrom(3) for the CH bond as that in CH4, yields an integrated cross section <(sigma)over bar>z=5.5X10(-18) cm for the CH stretching motion along the internuclear axis. Additional measurements of band position as a function of mixed isotope concentrations afford a stretching frequency of nu(i)=2816.2+/-0.9 cm(-1) for a single CH isolated in a monolayer of CD oscillators at 800 K. The frequency shift of nu(m)-nu(i)=16.0 cm(-1) is too large for dipole coupling theories to explain. The implications of the present findings with regard to applying IRS for quantitatively characterizing CVD diamondlike carbon films are discussed.