The macroscopic properties of monolayers of long chain amphiphile molecules assembled at the air-water interface have been studied for nearly a century.^1-3 However, it is only recently, by virtue of the application of grazing incidence X-ray diffraction (GIXD) to the study of these systems, that information has become available concerning the molecular packing in the several phases and mesophases that such a monolayer supports.⁴ This short report describes the use of a different technique, infrared external reflection spectroscopy, to study molecular conformation and collective molecular tilt in situ in monolayers of heneicosanol (C₂₁H₄₃OH) at the air-water interface. Surprisingly, the experimental data obtained provide strong qualitative evidence that the collective tilt ordering of heneicosanol molecules is different in relaxed and unrelaxed monolayers. This inference is supported by the results of molecular dynamics simulations, also described in this report. The experimental data and the results of the simulations support the inference that the very slow relaxation of the surface pressure which occurs when compression of a high density monolayer is stopped is due to the internal ordering of the long chain molecules coupled with molecular reorientation.