On the basis of CCSD(T) calculations, an accurate equilibrium geometry (unc
ertainties in bond lengths: ca. 0.0005 Angstrom) has been established for l
inear HC3P. The CP equilibrium bond length is 1.5515 Angstrom and thus slig
htly longer than in HCP. Harmonic vibrational wavenumbers, vibration-rotati
on coupling constants and l-type doubling constants are reported. Accurate
groundstate rotational constants are predicted for C-13 substituted species
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