Highly excited vibrational states of HCP X ¹Σ⁺ were investigated by stimulated emission pumping spectroscopy. Two distinct families of vibrational states were observed in the 13400 - 17500 cm^-1 energy region. One of them is "normal-mode-type" states, well characterized by polyads involving the bending (ω₂) and CP stretching (ω₃) vibrations. The other is delocalized "isomerization states" whose existence has been predicted by a recent theoretical study [J. Chem. Phys. 104, 10055 (1996)]. The present spectroscopic observations agree well with he theoretical predictions.