C-Chlorophosphaethyne (ClC≡P) has been generated by the pyrolysis of Cl3CPCl2 over granulated zinc at 550°C and the high-resolution spectrum in the region 4000-100 cm-1 has been recorded, analyzed, and assigned. Altogether, more than 6500 transitions have been assigned. The observed bands include all three fundamentals as well as a number of overtone, combination, and difference bands. For all the bands both the 35Cl and 37Cl isotopomers were observed, and for the ν3 band the 35Cl13C isotopomer was observed in natural abundance. The ground state rotational constants B0 and distortion constants D0 were found to be 0.10074626(10) and l.2544(10) × 10-8 cm-1 and 0.0981080(14) and 1.1950(16) × 10-8 cm-1 for the 35Cl and 37Cl isotopomers. respectively, and 0.10073766(72) and 1.158(11) × 10-8 cm-1 for the 13C species. After accounting for Fermi resonance effects the vibration-rotation parameters, αi, for all three fundamentals have been estimated and used to calculate the equilibrium B values; Be = 0.10094715(89) and 0.09830590(100) for the 35Cl and 37Cl isotopomers, respectively. The equilibrium geometry is calculated to be rC≡P = 155.26(61) and rC-Cl = 163.41(62) pm. The available fundamental frequencies of all three isotopomers have been used to calculate the harmonic force constants: fR(C-Cl) = 4.621; fr(C≡P) = 9.033; fRr = 0.499 aJ Å-2; and fα = 0.348 aJ.