Knowledge Bank

In attempts to find electronic Transitions in the diatomic metal carbides NiC, CrC, and HfC via R2PI spectroscopy by vaporizing the pure metal in a supersonic expansion of He seeded with 3% methane we have discovered optical transitions in a number of metal ligand complexes, some with more than one carbon atom. The polyatomic species for which we have recorded spectra are CrCCH, $NiCH3,CrCH3,Ni-C2H2,CrC3H2CrCH2$, and $HfC2$. The First Four of these have yielded by far the most interpretable spectra. In its ground state CrCCH is almost certainly linear with considerable ionic $(Cr\prime CCH-)$ character. All five {d} electron are most likely high spin coupled to give $X~6\Sigma +$. The optical spectrum of CrCCH between $11,000cm-1$ and $13,400cm-1$ displays a progression in the Cr-CCH stretch with $\omega e=426.4\pm 1.1cm-1$ and $\omega eXe=0.70\pm 0.17cm-1$. All of the main bands are split into three sub-bands with a spacing of approximately $10cm-1$ and $17cm-1$. This is suggestive of the expected zero field splitting of a $6\Sigma +$ state into its $\omega =1/2,3/2$, and 5/2 components and leads us to believe we are observing a $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}\Sigma -\leftarrow \mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}\Sigma +$ transition. Three of the six observed bands have been rotationally resolved, and analysis is under way. In the case of $CrCH3$, no upper state progression has been identified. The spectrum is dominated by sex bands within $500cm-1$ of the origin, which may be indicative of a sextet to sextet transection in which one of the states has residual orbital angular momentum that is causing a spin-orbit splitting into six spin components. These six bands are repeated about $510cm-1$ to the red when the region between $11,500cm-1$ and $12,500cm-1$ is scanned under conditions that make the molecular beam hot. We have deduced a ground state Cr-CH3 stretching frequency of $509.2\pm 1.4cm-1$ from these features. Nickel methyl displays sharper features than $CrCH3$ as well as an upper state progression with $\omega e=455.3cm-1$, which is presumably a $Ni-CH3$, stretching frequency. Finally, the vibrational spectrum of $Ni-C2H4$, is quite complicated, but the rotationally resolved spectrum of several bands is very simple.