Submillimeter-wave spectroscopy of phosphaalkynes:: HCCCP, NCCP, HCP, and DCP

The submillimeter-wave rotational spectra of the unstable phosphorus-bearing molecules HCCCP (phosphabutadiyne) and NCCP (C-cyanophosphaethyne) have been investigated in selected frequency regions between 490 and 815 GHz using the Cologne Terahertz Spectrometer. Both molecules were studied in their ground vibrational states. Additionally, vibrational satellites within the bending states v(4) = 1 and v(5) = 1 were recorded for NCCP. Furthermore, the ground state rotational spectra of the C-13 and N-15 isotopomers of NCCP were detected in natural abundance. The new measurements allowed us to evaluate the sextic centrifugal distortion constants for each isotopomer and vibrational state investigated. The pyrolysis reactions, through which HCCCP and NCCP were produced in situ, also yielded phosphaethyne, HCP, as a by-product. Some transitions of HCP and DCP were recorded in their ground vibrational states along with v(2) = 1 vibrational satellites of the former. (C) 2001 Academic Press.