1. 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

2. 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 = Å, Be = 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

3. Submillimeter Spectroscopy
Radiation Source: Phase-locked Gunn oscillators and Schottky diode multipliers ( 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

4. 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

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

6. 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

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

8. 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

9. 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
(24) D
(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
(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

10. CoS Bonding Electron configuration of [core]11s21d35p2
Magnetic Hyperfine Parameters
aCoS = MHz vs. a013d = 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

11. 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

12. 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

13. 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

14. 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