Electronic Transition of Electronic Transition of Ruthenium MonoxideRuthenium Monoxide

Na Wang, Y. W. Ng and A. S.-C. CheungDepartment of Chemistry

The University of Hong Kong

OutlineOutline• Introduction

• Experimental Setup

• Results

• Summary

IntroductionIntroductionWhy 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 RuOPrevious Studies on RuO• Raziunas et al.(J. Chem. Phys. 43 1010 (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 3Σ+ state o Obtained the bond length to be 1.70Å.

• Scullman and Thelin (J. Mol. Spec. 56 64 (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. 82 5584 (1985) )o Calculated the electronic structure of RuO using Multi-Configuration Self-Consistent-

Field (MC-SCF) wavefunctionso Predicted a 5Δ state ground state for RuO

Ground state of RuO is not confirmed yet

Gas-Phase Gas-Phase RuO RuO Production MethodProduction Method

Laser ablation/reaction free jet expansion

Molecule production:

Ru + N2O (~6% in Ar) → RuO + etc.

Ablation Laser : Nd:YAG, 10Hz, 532nm, 5mJ

Free Jet Expansion : i) backing pressure: 6 atm N2O (~6% in Ar)

ii) background pressure: 1x10-5 Torr

LIF spectrum in the visible region

Laser system: Optical Parametric Oscillator laser

Experimental SetupExperimental SetupSchematic Diagram of Laser Vaporization/ LIF Experimental Setup

Digital Delay/ Pulse Generator

Pulsed valve Controller

Nd:YAG Laser

Laser BeamVaporization laser Beam

Trigger

To Diffusion Pump

Ru rod

N2O in Argon

MonochromatorMonochromator

• Fix the wavelength of the OPO laser to pump the molecules

• Scan the grating in monochromator

• Wavelength resolved fluorescence spectrum

v’

v”

0

012

ΔG3/2

ΔG1/2

Excitation Laser

Scanning grating

ΔG1/2 ΔG3/2

Wavelength resolved fluorescence spectrum

MonochromatorMonochromator• 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 spectrumWithout monochromator filtering

Filtered fluorescence spectrumWith monochromator filtering

ResultsResultsThis work reported the

• [18.1] Ω = 4 – X 5Δ4 (“5526Å” system)

• [16.0] Ω = 5 – X 5Δ4

• [18.1] Ω = 3 – X 5Δ3 (“5532Å” system)

• [15.8] Ω = 4 – X5Δ3

transitions of RuO in the spectral region between 540-680nm using laser induced fluorescence (LIF) spectroscopy

Observed transitions of RuOObserved transitions of RuO

X5Δ4X5Δ3

[16.0]5Φ5

[18.1]Ω=4

[15.8]5Φ4

[18.1] Ω=3

v10

v0

v0

v10

v10

v10

18075 18085

15

4R(J)

Q(J)415

12

Wavenumber (cm-1)

5P(J)

The (0,0) band of the [18.1] Ω = 4 – X The (0,0) band of the [18.1] Ω = 4 – X 55ΔΔ33 transition of RuO transition of RuO

• P(5), Q(4), R(4) Ω’ = 4 – Ω” = 4

• [18.1] Ω = 4 – X 5Δ4

4

5

4

5Ω” = 4

J

Ω’ = 4

P(5)R(4) Q(4)

-1000 -500 0 500 1000 1500

18070 Band

v" =

1Vibrational separation (cm-1)

Laser

865cm-1

Resolved fluorescence spectrum of Resolved fluorescence spectrum of [18.1] Ω = 4 – X [18.1] Ω = 4 – X 55ΔΔ44

Observed transitions of RuOObserved transitions of RuO

X5Δ4X5Δ3

[16.0]5Φ5

[18.1]Ω=4

[15.8]5Φ4

[18.1] Ω=3

v10

v0

v0

v10

v10

v10

The (0,0) band of the [15.8] The (0,0) band of the [15.8] 55ΦΦ44 – X – X 55ΔΔ33 transition of RuO transition of RuO

• P(5), Q(4), R(3) Ω’ = 4 – Ω” = 3

• [15.8] 5Φ4 – X 5Δ3

15780 15790

31717 4

8

R(J)

Q(J)

P(J)5

Wavenumber (cm-1)

4

4

5Ω” = 3

JΩ’ = 4

P(5)R(3) Q(4)

3

Resolved fluorescence spectrum of Resolved fluorescence spectrum of [1[15.85.8] ] 55ΦΦ44 – X – X 55ΔΔ44

-1500 -1000 -500 0 500 1000 1500

Laser

856cm-115790 Band

Vibrational Separation (cm-1)v”

=1

856cm-1

Summary on molecular Constants for RuO (cmSummary on molecular Constants for RuO (cm-1-1))

Parameter

[18.1] Ω=3 [18.1] Ω=4[15.8] Ω=4

X 5Δ3 X 5Δ4

Toa+18064.99(

2)18881.18(1)

a+15788.25(2)

a 0

ΔG1/2 784.87 795.19 983.69856.27(2

)855.82(

2)

Be 0.3813 0.3822 0.3884 0.4139 0.4148

re (Å) 1.787 1.785 1.771 1.715 1.714

αe 0.0014 0.0011 0.0051 0.0022 0.0035

Molecular orbital energy level diagramMolecular orbital energy level diagram

Ground State Configuration of RuC: (11σ)2(5π)4(2δ)4 1Σ+

RuC

11σ

5π

12σ6π

13σ

Ru C

4d

5s

2p2δ

σ

δπ

σ

σ

π

RuNN

Ground State Configuration of RuC: (11σ)2(5π)4(2δ)4(12σ)1 2Σ+

Ground State Configuration of RuO: (11σ)2(5π)4(2δ)4(12σ)2 1Σ+

ORuO

(11σ)2(5π)4(2δ)4(12σ)1(6π)1 3Π

Do not contribute to states with Ω =3 or 4

Molecular orbital energy level diagramMolecular orbital energy level diagram

Ground State Configuration of RuF: (11σ)2(5π)4(2δ)3(6π)3(12σ)1 4Φ9/2

RuF

11σ

5π

12σ

6π

13σ

Ru F

4d

5s

2p2δ

σ

δπ

σ

σ

π

Molecular orbital energy level diagramMolecular orbital energy level diagram

FeO is isoelectronic to RuO

Ground State Configuration of FeO: (8σ)2(3π)4(1δ)3(9σ)1(5π)2 5Δ

FeO

8σ

3π

9σ4π

10σ

Fe O

3d

4s

2p1δ

σ

δπ

σ

σ

π

Molecular orbital energy level diagramMolecular orbital energy level diagram

Ground State Configuration of RuO: (11σ)2(5π)4(2δ)3(12σ)1(6π)2 5Δ

RuO

11σ

5π

12σ6π

13σ

Ru O

4d

5s

2p2δ

σ

δπ

σ

σ

π

Ground State AnalysisGround State Analysis• Ground State Configuration:

(11σ)2(5π)4(2δ)3(12σ)1(6π)1 5Δ

• Number of electrons in δ MO is more than half-filled inverted 5Δ

• Transitions obtained are from lower state Ω = 3 and Ω = 4 inverted 5Δ

Ground State of RuO : X5Δ4

Comparison of Ru compounds Comparison of Ru compounds Molecule RuB RuC RuN RuO RuF

Electronic configuratio

nδ3 δ4 δ4σ1 δ3σ1π2 δ3π3σ1

Symmetry 2Δ5/21+ 2+ 5Δ4

4Φ9/2

Be (cm-1) 0.5834 0.6072 0.5545 0.4148 0.2866

re (Å) 1.706 1.608 1.571 1.714 1.916

ΔG1/2 (cm-1) 911.0 1029.6 1108.3 855.8 534.0

SummarySummary• Reported four electronic transition system of RuO

o [18.1] Ω = 4 – X 5Δ4

o [16.0] Ω = 5 – X 5Δ4

o [18.1] Ω = 3 – X 5Δ3

o [15.8] Ω = 4 – X5Δ3

• Ground state symmetry: X 5Δ4

• Equilibrium bond length, re = 1.714Å