Electronic Transition of Ruthenium Monoxide Na Wang, Y. W. Ng and A. S.-C. Cheung Department of Chemistry The University of Hong Kong

Outline Introduction Experimental Setup Results Summary

Introduction Why we study diatomic Transition Metal Monoxides? Transition metal monoxides play important roles in catalysis, and high temperature chemistry Diatomic transition metal molecule is the simplest model for studying more complicated transition metal compounds The near degeneracy of the d orbitals and the various spin configurations give rise to many low-lying electronic states with high spin multiplicity  increase complexity in identifying ground state

Previous Studies on RuO Raziunas et al.(J. Chem. Phys (1965)) o Studied the emission spectrum of RuO molecule by using a low-current dc arc as the light source o Reported ground state of RuO as 3 Σ + state o Obtained the bond length to be 1.70Å. Scullman and Thelin (J. Mol. Spec (1975) ) o Performed emission experiment using a hollow cathode lamp o Analyzed three subsystems called “5526Å”, “5532Å” and “5544Å” o Obtained the bond length as 1.718Å. Krauss and Stevens (J. Chem. Phys (1985) ) o Calculated the electronic structure of RuO using Multi-Configuration Self-Consistent-Field (MC-SCF) wavefunctions o Predicted a 5 Δ state ground state for RuO Ground state of RuO is not confirmed yet

Gas-Phase RuO Production Method Laser ablation/reaction free jet expansion Molecule production: Ru + N 2 O (~6% in Ar) → RuO + etc. Ablation Laser : Nd:YAG, 10Hz, 532nm, 5mJ Free Jet Expansion : i) backing pressure: 6 atm N 2 O (~6% in Ar) ii) background pressure: 1x10 -5 Torr LIF spectrum in the visible region Laser system: Optical Parametric Oscillator laser

Experimental Setup Schematic Diagram of Laser Vaporization/ LIF Experimental Setup Digital Delay/ Pulse Generator Pulsed valve Controller Nd:YAG Laser Laser Beam Vaporization laser Beam Trigger To Diffusion Pump Ru rod N 2 O in Argon

Monochromator Fix the wavelength of the OPO laser to pump the molecules Scan the grating in monochromator Wavelength resolved fluorescence spectrum v’ v” Δ G 3/2 Δ G 1/2 Excitation Laser Scanning grating Δ G 1/2 Δ G 3/2 Wavelength resolved fluorescence spectrum

Monochromator Serve as an optical filter Set the grating in monochromator at a particular wavelength Only small spectral region is detected by PMT Remove unwanted scattering light 8 Total fluorescence spectrum Without monochromator filtering Filtered fluorescence spectrum With monochromator filtering

Results This work reported the [18.1] Ω = 4 – X 5 Δ 4 (“5526Å” system) [16.0] Ω = 5 – X 5 Δ 4 [18.1] Ω = 3 – X 5 Δ 3 (“5532Å” system) [15.8] Ω = 4 – X 5 Δ 3 transitions of RuO in the spectral region between nm using laser induced fluorescence (LIF) spectroscopy

Observed transitions of RuO X5Δ4X5Δ4 X5Δ3X5Δ3 [16.0] 5 Φ 5 [18.1]Ω=4 [15.8] 5 Φ 4 [18.1] Ω=3 v 1 0 v 0 v 0 v 1 0 v 1 0 v 1 0

The (0,0) band of the [18.1] Ω = 4 – X 5 Δ 3 transition of RuO P(5), Q(4), R(4)  Ω’ = 4 – Ω” = 4 [18.1] Ω = 4 – X 5 Δ Ω” = 4 J Ω’ = 4 P(5)R(4) Q(4)

Resolved fluorescence spectrum of [18.1] Ω = 4 – X 5 Δ 4

Observed transitions of RuO X5Δ4X5Δ4 X5Δ3X5Δ3 [16.0] 5 Φ 5 [18.1]Ω=4 [15.8] 5 Φ 4 [18.1] Ω=3 v 1 0 v 0 v 0 v 1 0 v 1 0 v 1 0

The (0,0) band of the [15.8] 5 Φ 4 – X 5 Δ 3 transition of RuO P(5), Q(4), R(3)  Ω’ = 4 – Ω” = 3 [15.8] 5 Φ 4 – X 5 Δ Ω” = 3 J Ω’ = 4 P(5)R(3) Q(4) 3

Resolved fluorescence spectrum of [15.8] 5 Φ 4 – X 5 Δ 4 v”=1 856cm -1

Summary on molecular Constants for RuO (cm -1 ) Parameter[18.1] Ω=3[18.1] Ω=4[15.8] Ω=4X 5 Δ 3 X 5 Δ 4 ToTo a (2) (1)a (2) a0 ΔG 1/ (2)855.82(2) BeBe r e (Å) αeαe

Molecular orbital energy level diagram Ground State Configuration of RuC: (11σ) 2 (5π) 4 (2δ) 4  1 Σ + RuC 11σ 5π5π 12σ 6π6π 13σ RuC 4d 5s 2p 2δ2δ σ δ π σ σ π RuN N Ground State Configuration of RuC: (11σ) 2 (5π) 4 (2δ) 4 (12σ) 1  2 Σ + Ground State Configuration of RuO: (11σ) 2 (5π) 4 (2δ) 4 (12σ) 2  1 Σ + O RuO (11σ) 2 (5π) 4 (2δ) 4 (12σ) 1 (6π) 1  3 Π Do not contribute to states with Ω =3 or 4

Molecular orbital energy level diagram Ground State Configuration of RuF: (11σ) 2 (5π) 4 (2δ) 3 (6π) 3 (12σ) 1  4 Φ 9/2 RuF 11σ 5π5π 12σ 6π6π 13σ RuF 4d 5s 2p 2δ2δ σ δ π σ σ π

Molecular orbital energy level diagram FeO is isoelectronic to RuO Ground State Configuration of FeO: (8σ) 2 (3π) 4 (1δ) 3 (9σ) 1 (5π) 2  5 Δ FeO 8σ8σ 3π3π 9σ9σ 4π4π 10σ FeO 3d 4s 2p 1δ1δ σ δ π σ σ π

Molecular orbital energy level diagram Ground State Configuration of RuO: (11σ) 2 (5π) 4 (2δ) 3 (12σ) 1 (6π) 2  5 Δ RuO 11σ 5π5π 12σ 6π6π 13σ RuO 4d 5s 2p 2δ2δ σ δ π σ σ π

Ground State Analysis Ground State Configuration: (11σ) 2 (5π) 4 (2δ) 3 (12σ) 1 (6π) 1  5 Δ Number of electrons in δ MO is more than half-filled  inverted 5 Δ Transitions obtained are from lower state Ω = 3 and Ω = 4  inverted 5 Δ Ground State of RuO : X 5 Δ 4

Comparison of Ru compounds MoleculeRuBRuCRuNRuORuF Electronic configuration δ3δ3 δ4δ4 δ4σ1δ4σ1 δ3σ1π2δ3σ1π2 δ3π3σ1δ3π3σ1 Symmetry 2 Δ 5/2 1+1+2+2+ 5Δ45Δ4 4 Φ 9/2 B e (cm -1 ) r e (Å) ΔG 1/2 (cm -1 )

Summary Reported four electronic transition system of RuO o [18.1] Ω = 4 – X 5 Δ 4 o [16.0] Ω = 5 – X 5 Δ 4 o [18.1] Ω = 3 – X 5 Δ 3 o [15.8] Ω = 4 – X 5 Δ 3 Ground state symmetry: X 5 Δ 4 Equilibrium bond length, r e = 1.714Å