The Fourier transform microwave spectrum of the arsenic dicarbide radical (CCAs: X̃2Π1/2) and its 13C isotopologues

M. Sun, D. J. Clouthier, Lucy M Ziurys

Research output: Contribution to journalArticle

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Abstract

The pure rotational spectrum of the CCAs radical in its ground electronic and spin state, X̃2Π1/2, has been measured using Fourier transform microwave techniques in the frequency range of 12-40 GHz. This species was created in a supersonic expansion from a reaction mixture of AsCl3 and C2H2 or CH4 diluted in high pressure argon, using a pulsed nozzle containing a dc discharge source. Three rotational transitions were measured for the main isotopologue, 12C12CAs, in the ω=1/2 ladder; both lambda-doubling and arsenic (I=3/2) hyperfine interactions were observed in these spectra. In addition, two to four rotational transitions were recorded for the 13C13CAs, 13C12CAs, and 12C13CAs species. In these three isotopologues, hyperfine splittings were also resolved arising from the 13C nuclei (I=1/2), creating complex spectral patterns. The CCAs spectra were analyzed with a case (a) Hamiltonian, and effective rotational, lambda-doubling, and arsenic and carbon-13 hyperfine constants were determined for the ω=1/2 ladder. From the effective rotational constants of the four isotopologues, an r m(1) structure has been derived with rC-C=1.287 Å and rC-As=1.745 Å. These bond lengths indicate that the predominant structure for arsenic dicarbide is C=C=As·, with some contributing C≡C and C≡As triple bond characters. The hyperfine constants established in this work indicate that about 2/3 of the unpaired electron density lies on the arsenic atom, with the remaining percentage on the terminal carbon. The value of the arsenic quadrupole coupling constant (eqQ=-202 MHz) suggests that the As-C bond has a mixture of covalent and ionic characters, consistent with theoretical predictions that both π backbonding and electron transfer play a role in creating a linear, as opposed to a cyclic, structure for certain heteroatom dicarbides.

Original languageEnglish (US)
Article number224317
JournalThe Journal of Chemical Physics
Volume131
Issue number22
DOIs
StatePublished - 2009

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microwave spectra
Arsenic
arsenic
Fourier transforms
Microwaves
Ladders
ladders
Carbon
Hamiltonians
carbon 13
Argon
rotational spectra
Bond length
nozzles
Carrier concentration
Nozzles
electron transfer
quadrupoles
frequency ranges
argon

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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The Fourier transform microwave spectrum of the arsenic dicarbide radical (CCAs : X̃2Π1/2) and its 13C isotopologues. / Sun, M.; Clouthier, D. J.; Ziurys, Lucy M.

In: The Journal of Chemical Physics, Vol. 131, No. 22, 224317, 2009.

Research output: Contribution to journalArticle

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abstract = "The pure rotational spectrum of the CCAs radical in its ground electronic and spin state, X̃2Π1/2, has been measured using Fourier transform microwave techniques in the frequency range of 12-40 GHz. This species was created in a supersonic expansion from a reaction mixture of AsCl3 and C2H2 or CH4 diluted in high pressure argon, using a pulsed nozzle containing a dc discharge source. Three rotational transitions were measured for the main isotopologue, 12C12CAs, in the ω=1/2 ladder; both lambda-doubling and arsenic (I=3/2) hyperfine interactions were observed in these spectra. In addition, two to four rotational transitions were recorded for the 13C13CAs, 13C12CAs, and 12C13CAs species. In these three isotopologues, hyperfine splittings were also resolved arising from the 13C nuclei (I=1/2), creating complex spectral patterns. The CCAs spectra were analyzed with a case (a) Hamiltonian, and effective rotational, lambda-doubling, and arsenic and carbon-13 hyperfine constants were determined for the ω=1/2 ladder. From the effective rotational constants of the four isotopologues, an r m(1) structure has been derived with rC-C=1.287 {\AA} and rC-As=1.745 {\AA}. These bond lengths indicate that the predominant structure for arsenic dicarbide is C=C=As·, with some contributing C≡C and C≡As triple bond characters. The hyperfine constants established in this work indicate that about 2/3 of the unpaired electron density lies on the arsenic atom, with the remaining percentage on the terminal carbon. The value of the arsenic quadrupole coupling constant (eqQ=-202 MHz) suggests that the As-C bond has a mixture of covalent and ionic characters, consistent with theoretical predictions that both π backbonding and electron transfer play a role in creating a linear, as opposed to a cyclic, structure for certain heteroatom dicarbides.",
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