LAUSR

Abstract Trideuterated 1-phosphapropyne ( CD 3 CP ) has been produced by co-pyrolysis of phosphorus trichloride and esadeuterated ethane. The rotational spectra of CD 3 CP in the ground and the low-lying vibrational states v 8 (CCP bending mode) and 2 v 8 have been investigated in the millimeter-wave region. Very accurate values of the quartic centrifugal distortion constants D J and D J K and of the sextic distortion constants H J K and H K J have been obtained for the ground state. l-type resonance effects have been taken into account in the analysis of the spectra of the degenerate bending states, so that the energy difference between the v 8 | l |  = 20, and v 8 | l |  = 22 states could be determined, together with a number of spectroscopic constants involved in the l-type resonance. Moreover, for the parent isotopologue CH 3 CP a new set of excited-state lines ( v 8  = 1, 2 and v 4  = 1) were recorded up to 330 GHz, and a global analysis including all available rotational and rovibrational transitions related to the ground and v 8  = 1, 2 states has been performed. A satisfactory fit could only be obtained by making a reassignment of the few transition wavenumbers previously measured for the 2 ν 8 0 ← ν 8 ± 1 hot band [M.K. Bane et al., J. Mol. Spectrosc. 275 (2012) 9–14]. The experimental work has been combined with quantum-chemical computations. Quadratic and cubic force constants of 1-phosphapropyne have been calculated at MP2 level of theory with a basis set of triple-ζ quality. A semi-experimental equilibrium structure has been derived by correcting experimental ground-state rotational constants by means of theoretical vibration-rotation interaction constants.