Just for completeness, I calculated the Fourier transform (as an FFT of length 1024, zero padded) on the original data, and the output is shown on the attached plot.
As you can see, the autocorrelation function does quite a bit better than the FFT to distinguish the frequency of interest, but there are other peaks in the autocorrelation function nearly as large, so it would be difficult to have much confidence in the result.
