Michael A. Flory Shawn K. McLamarrah Lucy M. Ziurys The Secrets of Cobalt Bonding: The Pure Rotational Spectrum of CoS (X4Di) Michael A. Flory Shawn K. McLamarrah Lucy M. Ziurys Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

What makes CoS interesting? Bonding important in surface chemistry and catalysis but transtion metal sulfides not well studied The ground state is uncertain Analogy to CoO gives X 4Di, but NiH (X 2D) while NiF (X 2P) Theoretical predictions disagree Anderson, Hong, and Smialek (1987): ASED-MO X 4S, re = 2.13 Å, Be = 5.37 GHz Bauschlicher and Maitre (1994): ab initio X 4D, re = 1.9802 Å, Be = 6.2124 GHz Bridgeman and Rothery (1999): DFT X 4D, re = 1.96 Å, Be = 6.34 GHz Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Submillimeter Spectroscopy Radiation Source: Phase-locked Gunn oscillators and Schottky diode multipliers (65-660 GHz) Gaussian beam optics utilized to minimize radiation loss Reaction Chamber: Double walled, steel cell which contains a Broida-type oven Detector: InSb bolometer Radiation is modulated at 25kHz and detected at 2f Block diagram of spectrometer Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Gas-Phase Synthesis of CoS Co vapor produced in high temp Broida-type oven m.p. = 1495 °C Reacted with H2S or CS2 (20 mtorr) No d.c. discharge required No carrier gas used Initial search ~40 GHz based on estimated B value Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

CoS (X ? ? ) 4Di 2Di W = 7/2 W = 1/2 W = 3/2 W = 5/2 v = 1 v = 2 v = 0 J = 38.5 37.5 Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

4Di Energy Levels W = L + S J ≥ W Energy 2ASO 4ASO 6ASO W = 7/2 Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

The Four Spin Components Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Sample transition frequencies for Co32S (4Di; J = 16.515.5; in MHz) 509 Total Lines Recorded for v = 0 Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Ĥeff = ĤRot + ĤSO + ĤSS + Ĥld + Ĥmhf + ĤeqQ Fitted CoS Constants Fit globally using a Hund’s case (a) coupling scheme: Ĥeff = ĤRot + ĤSO + ĤSS + Ĥld + Ĥmhf + ĤeqQ B0 6228.4665(24) D 0.0040523(11) A -4,750,000(120,000) Ad -0.86(11) l 385,000(95,000) ld 0.38(25) h 63,000(22,000) ñD 19.774(29) a 663.8(5.2) b -77(22) b+c -211.7(9.7) eqQ -171(93) rms 0.328 r0 1.9776476(12) Å Components from v>0 and Co34S fit individually using case (c) scheme In MHz; Errors are 3s Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

CoS Bonding Electron configuration of [core]11s21d35p2 Magnetic Hyperfine Parameters aCoS = 663.8 MHz vs. a013d = 617.9 MHz Shows that d orbital is non-bonding c = -135 MHz  5p orbital is 45% Cobalt Agrees with 40-60% metal character calculation by Bridgeman for metal oxide 4p Mixture of ionic and covalent character Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Oxide vs Sulfide Bondlengths Sulfides are incomplete Similar trend emerging CoS bond quite short MF and MCl also similar Short bond also seen in CoCl Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Bonds of 2nd vs. 3rd row elements -Similar bonding trends observed for 2nd and 3rd row main group elements Exception: Large drop in bondlength from FeX to CoX in 3rd row compared to 2nd row Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Anderson, Hong, Smialek (1987) M 4p Stabilization Shortened bondlength explained by orbital energies: 3p orbitals ≈ metal orbitals At Cobalt: M 3d < Ligand 3p Co 4p sufficiently low in E to stabilize 4p and 11s when bonding with 3rd row elements Anderson, Hong, Smialek (1987) Department of Chemistry Department of Astronomy Steward Observatory University of Arizona

Conclusions …and Beginings Ground state is identified as 4Di Bondlength of CoS is significantly shorter than FeS This is explained by interaction of Co 4p and non-metal 3p orbitals …and Beginings Measure and analyze CoSH and CoOH spectra Department of Chemistry Department of Astronomy Steward Observatory University of Arizona