The Infrared Spectrum of Chlorophosphaethyne, ClC≡P

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, α_i, for all three fundamentals have been estimated and used to calculate the equilibrium B values; B_e = 0.10094715(89) and 0.09830590(100) for the ³⁵Cl and ³⁷Cl isotopomers, respectively. The equilibrium geometry is calculated to be r_C≡P = 155.26(61) and r_C-Cl = 163.41(62) pm. The available fundamental frequencies of all three isotopomers have been used to calculate the harmonic force constants: f_R(C-Cl) = 4.621; f_r(C≡P) = 9.033; f_Rr = 0.499 aJ Å^-2; and f_α = 0.348 aJ.