First spectroscopic investigation of the 4d transition metal monocarbide MoC

Abstract

The first optical spectroscopic investigation of MoC has revealed a complicated vibronic spectrum consisting of about 35 bands between 17 700 and 24 000 cm−1. Analysis has shown the ground state to be the Ω=0+ spinorbit component of a Σ3− state that derives from a 10σ211σ25π42δ2 configuration. The X 3Σ0+− rotational constant for Mo9812C was determined to be B0=0.553 640±0.000 055 cm−1, giving r0=1.687 719±0.000 084 Å. Consideration of spin-uncoupling effects in the X 3Σ− state requires that this value be revised to r0=1.6760 Å, which represents our best estimate of the true Mo–C bond length. Spectroscopic constants were also extracted for six other major isotopic modifications of MoC in this mass resolved experiment. All rotationally resolved transitions were found to originate from the ground state and terminate in electronic states with Ω=1. An attempt is made to classify the observed transitions into band systems, to rationalize the complexity of the spectrum, and to understand the bonding from a molecular orbital point of view.

Resonant two-photon ionization spectroscopy of jet-cooled PdC

“…The important molecular orbitals are formed using the 4d Pd and 5s Pd orbitals of palladium and the 2s C and 2p C orbitals of carbon. As has been discussed in other papers from this group [13][14][15] and elsewhere, these orbitals combine to give low-lying 10, 11, and 5 orbitals. The 10 and 11 orbitals are somewhat difficult to characterize without detailed calculations, but the 10 orbital is probably mainly carbon 2s in character while the 11 orbital is probably a bonding orbital with significant contributions from the 4d Pd and 2p C orbitals.…”

“…Recently laser spectroscopic studies of FeC, 13 MoC, 14 and RuC ͑Ref. 15͒ have been published from this research group, and a paper on the optical spectra of NiC is in preparation.…”

Nuclear hyperfine structure in the X3Σ+ state of 91ZrC

“…With the much lower temperature the 4 P i assignment of the ground state was unambiguous, and led to the interesting result that the carbon 2p molecular orbitals lie at almost the same energy as the metal 5s. Since then a number of monocarbides have been found, most notably FeC [12,13], CoC [14,15], NiC [16], NbC [17], MoC [18], PdC [19], and WC [20].…”

The electronic structure of MoC and WC by anion photoelectron spectroscopy

“…The ground state properties of MoC have been well discussed by Morse et al in their recent spectroscopic investigation. 10 Figure 3 shows schematically the valence molecular orbitals ͑MOs͒ of MoC and the ground state configuration, 1 2 1 4 2 2 1␦ 2 , where 1 2 is mainly the C 2s, 1 and 2 are bonding MOs between C 2p and Mo 5d, 1␦ and 3 are nonbonding MOs from Mo 4d and 5s, respectively.…”

“…The first spectroscopic investigation of MoC has been just reported by Morse and co-workers, 10 who also provided an excellent discussion of the chemical bonding between the 4d transition metals and C and its trend across the periodic table. Due to the strong relativistic effects, the 5d transition metals are expected to show different behaviors in their bonding to C. We obtained vibrationally resolved PES spectra of MoC Ϫ and WC Ϫ at two photon energies, 532 ͑2.331 eV͒ and 355 nm ͑3.496 eV͒.…”