The rotational spectrum of the CCP (XΠr2) radical and its C13 isotopologues at microwave, millimeter, and submillimeter wavelengths

Abstract

The pure rotational spectrum of CCP (X (2)Pi(r)) has been measured at microwave, millimeter, and submillimeter wavelengths (17-545 GHz), along with its (13)C isotopologues ((13)C(13)CP, C(13)CP, and (13)CCP). The spectra of these species were recorded using a combination of millimeter/submillimeter direct absorption methods and Fourier transform microwave (FTMW) techniques. The phosphorus dicarbides were created in the gas phase from the reaction of red phosphorus and acetylene or methane in argon in an ac discharge for the direct absorption experiments, and using PCl(3) as the phosphorus source in a pulsed dc nozzle discharge for the FTMW measurements. A total of 35 rotational transitions were recorded for the main isotopologue, and between 2 and 8 for the (13)C-substituted species. Both spin-orbit components were identified for CCP, while only the Omega = 12 ladder was observed for (13)C(13)CP, C(13)CP, and (13)CCP. Hyperfine splittings due to phosphorus were observed for each species, as well as carbon-13 hyperfine structure for each of the (13)C-substituted isotopologues. The data were fitted with a Hund's case (a) Hamiltonian, and rotational, fine structure, and hyperfine parameters were determined for each species. The r(m)(1) bond lengths established for CCP, r(C-C) = 1.289(1) A and r(C-P) = 1.621(1) A, imply that there are double bonds between both the two carbon atoms and the carbon and phosphorus atoms. The hyperfine constants suggest that the unpaired electron in this radical is primarily located on the phosphorus nucleus, but with some electron density also on the terminal carbon atom. There appears to be a minor resonance structure where the unpaired electron is on the nucleus of the end carbon. The multiple double bond structure forces the molecule to be linear, as opposed to other main group dicarbides, such as SiC(2), which have cyclic geometries.

A high-resolution photoelectron imaging and theoretical study of CP− and C2P−

“…The peaks X and a have similar intensities and they correspond to the spin-orbit splitting of the 2 Π 1/2 and 2 Π 3/2 states, in agreement with previous reports of the neutral C 2 P spectroscopy. [17][18][19] Peaks b and c match the measured frequencies for the second quanta of the bending modes of the lower and higher spin-orbit states, respectively. The uneven spacing of this mode in the two spin-orbit states is due to the Renner-Teller effects, as reported previously.…”

“…[13][14][15][16] The observation and spectroscopic characterization of C 2 P have been much more recent by Clouthier and co-workers. [17][18][19] The ground state of C 2 P was found to be linear in a 2 Π 1/2 state with a higher spin-orbit state ( 2 Π 3/2 ) being 17.49 meV (141 cm 1 ) higher in energy. 19 The stretching modes and rotational constants of C 2 P were determined along with a detailed Renner-Teller analysis.…”

“…[17][18][19] The ground state of C 2 P was found to be linear in a 2 Π 1/2 state with a higher spin-orbit state ( 2 Π 3/2 ) being 17.49 meV (141 cm 1 ) higher in energy. 19 The stretching modes and rotational constants of C 2 P were determined along with a detailed Renner-Teller analysis. 18 In contrast, very little is known about the corresponding CP and C 2 P anions.…”

The impact of recent advances in laboratory astrophysics on our understanding of the cosmos

“…Recent discoveries, such as CCP or AlOH, have relied on such work, in particular those employing millimeter direct absorption and Fourier transform microwave methods (e.g., Apponi et al 1993;Halfen et al 2009). Many potential species of this type are highly reactive, and require unusual, non-equilibrium synthesis methods.…”

Division Xii/Commission 14/Working Group on Molecular Data

“…The study of the rotational spectrum of C 2 P (Halfen et al 2009a) laid the ground work for its detection in the circumstellar envelope of CW Leo. This detection, in turn, suggests that molecules such as C 2 F, C 2 Cl, C 3 F, and C 3 Cl may be detectable as well.…”