Highly excited vibrational states of HCP (X) over tilde (1) Sigma(+) 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 (omega(2)) and CP stretching (omega(3)) 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 the theoretical predictions.