Rotational analysis of the $3_0^1 $31 band of the $\tilde A{}^6\Sigma ^ + \leftarrow \tilde X{}^6\Sigma ^ + $Ã6Σ+←X̃6Σ+ system of CrCCH

Pure rotational spectroscopy of the CrC (X3Σ−) and CrCCH (X̃ 6Σ+) radicals has been conducted using millimeter/sub-millimeter direct absorption methods in the frequency range 225-585 GHz. These species were created in an AC discharge of Cr(CO)6 and either methane or acetylene, diluted in argon. Spectra of the CrCCD were also recorded for the first time using deuterated acetylene as the carbon precursor. Seven rotational transitions of CrC were measured, each consisting of three widely spaced, fine structure components, arising from spin-spin and spin-rotation interactions. Eleven rotational transitions were recorded for CrCCH and five for CrCCD; each transition in these cases was composed of a distinct fine structure sextet. These measurements confirm the respective 3Σ− and 6Σ+ ground electronic states of these radicals, as indicated from optical studies. The data were analyzed using a Hund’s case (b) Hamiltonian, and rotational, spin-spin, and spin-rotation constants have been accurately determined for all three species. The spectroscopic parameters for CrC were significantly revised from previous optical work, while those for CrCCH are in excellent agreement; completely new constants were established for CrCCD. The chromium-carbon bond length for CrC was calculated to be 1.631 Å, while that in CrCCH was found to be rCr—C = 1.993 Å — significantly longer. This result suggests that a single Cr—C bond is present in CrCCH, preserving the acetylenic structure of the ligand, while a triple bond exists in CrC. Analysis of the spin constants suggests that CrC has a nearby excited 1Σ+ state lying ∼16 900 cm−1 higher in energy, and CrCCH has a 6Π excited state with E ∼ 4800 cm−1.

Section: Discussionsupporting

confidence: 70%

“…24,26 The ground state of CrCCH is 6 Σ + . As illustrated in Figure 4, each rotational level for this term, indicated by N, is split into six fine structure components, labeled by J.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Millimeter-wave spectroscopy of CrC (X3Σ−) and CrCCH (X̃ 6Σ+): Examining the chromium-carbon bond

Min

Ziurys

2016

“…To better understand how metal centers activate C− −H/C bonds, spectroscopy of transition metal-hydrocarbon species formed in gas phase reactions has recently attracted considerable attention. Metal ion-hydrocarbon species are largely investigated by infrared or ultraviolet-visible photodissociation or photoelectron spectroscopy, whereas metal atom-hydrocarbon radicals are mainly studied by resonant two-photon ionization and dispersed fluorescence, [35][36][37][38] Fourier transform microwave, 39 and mass analyzed threshold ionization (MATI) spectroscopy. [40][41][42][43][44][45][46][47][48] Spectroscopic measurements probe state specific energies and structures of short-lived species, which are vital for gaining insight into reaction mechanisms and electronic and structural characteristics for efficient bond activation at metal centers.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by association and carbon-carbon bond cleavage of isoprene

Cao

Hewage

Yang

2018

Right click to open a feedback form in a new tab to let us know how this document benefits you.La atom reaction with isoprene is carried out in a laser-vaporization molecular beam source. The reaction yields an adduct as the major product and C− −C cleaved and dehydrogenated species as the minor ones. La(C 5 H 8 ), La(C 2 H 2 ), and La(C 3 H 4 ) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of all three species exhibit a strong origin band and several weak vibronic bands corresponding to La-ligand stretch and ligand-based bend excitations. La(C 5 H 8 ) is a five-membered metallacycle, whereas La(C 2 H 2 ) and La(C 3 H 4 ) are three-membered rings. All three metallacycles prefer a doublet ground state with a La 6s 1 -based valence electron configuration and a singlet ion. The five-membered metallacycle is formed through La addition and isoprene isomerization, whereas the two three-membered rings are produced by La addition and insertion, hydrogen migration, and carbon-carbon bond cleavage. Published by AIP Publishing. https://doi.

“…Therefore, a reliable identification of structural isomers and electronic states generally requires confirmation by spectroscopic measurements. Metal ion-hydrocarbon species were largely investigated with infrared or ultraviolet-visible photodissociation or photoelectron spectroscopy, whereas metal atom-hydrocarbon radicals were mainly studied through resonant two-photon ionization and dispersed fluorescence [58][59][60][61] and Fourier transform microwave spectroscopy. 62 We have recently reported the mass-analyzed threshold ionization (MATI) spectroscopy and formation of the metal-hydrocarbon radicals produced by the lanthanide-mediated C− −C and C− −H bond activation of several small alkenes and alkynes.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by C—H and C—C bond activation of 1-pentene and 2-pentene

Cao

Zhang

Nyambo

et al. 2018

La atom reactions with 1-pentene and 2-pentene are carried out in a laser-vaporization molecular beam source. The two reactions yield the same metal-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage of the pentene molecules. The dehydrogenated species La(CH) is the major product, whereas the carbon-carbon bond cleaved species La(CH) and La(CH) are the minor ones. La(CH) is also observed and is presumably formed by La(CH) addition to a second pentene molecule. La(CH) and La(CH) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species from the two reactions exhibit the same transitions. Adiabatic ionization energies and metal-ligand stretching frequencies are determined for the two species, and additional methyl bending and torsional frequencies are measured for the larger one. Five possible isomers are considered for La(CH), and a C metallacyclopentene (Iso A) is identified as the most possible isomer. La(CH) is confirmed to be a C metallacyclopropene. The ground electronic state of each species is a doublet with a La 6s-based electron configuration, and ionization yields a singlet state. The formation of the lanthanacyclopentene includes La addition to the C=C double bond, La insertion into two C(sp)-H bonds, and concerted dehydrogenation. For the 2-pentene reaction, the formation of the five-membered ring may also involve 2-pentene to 1-pentene isomerization. In addition to the metal addition and insertion, the formation of the three-membered metallacycle from 1-pentene includes C(sp)-C(sp) bond breakage and hydrogen migration from La to C(sp), whereas its formation from 2-pentene may involve the ligand isomerization.