Electronic transitions of Yttrium Monoxide Allan S.-C. Cheung, Y. W. Ng, Na Wang and A. Clark Department of Chemistry University of Hong Kong OSU International Symposium on Molecular Spectroscopy 19 June, 2013 (WK11) Paper: WK11

Acknowledgements Ph.D. Students:Mr. Tony Y. W. Ng Miss Na Wang Exchange Student:Mr. Andrew Clark U. of Edinburgh Funding Agents: Research Grants Council, HKSAR Committee on Research & Conference Grants, HKU

Introduction Why are we interested in YO and (ZrO and ScO)? Astrophysical interests  Presence in the atmosphere of cool M- and S- type stars Murty, P. S., Astrophys. Lett. & Comm. 23, 7 (1982) Murty, P. S., Astrophys. & Space Science 94, 295 (1983) Spectroscopic interests  Molecular and electronic structure  (n+1)s 2 nd 1 model system for studying participation of d orbital  Y has 5s 2 4d 1, Sc 4s 2 3d 1 and Zr 5s 2 4d 2 electronic configurations S.R. Langhoff, et al, Annu. Rev. Phys. Chem. 39, 181 (1988)

Introduction Previous studies on YO:  Meggers et. al., J. Res. NBS 6, 239 (1931).  First spectrum of YO produced by electric arc discharge.  Chalek et. al., Chem. Phys. 19, 59(1977).  Recorded A’ 2  - X 2 Σ + transition in chemiluminescent reactions of YO.  Observed weak C 2 Π - X 2 Σ + transition between 280 nm and 320 nm, only low resolution spectrum, no detailed analysis. Bernard et. al., Ap. J. Suppl. Ser. 52, 443 (1983). – Emission spectroscopy using hollow cathode discharge technique. B 2 Σ + State r e = Å A 2 Π Stater e = Å X 2 Σ + Stater e = Å Langhoff et al., J. Chem. Phys. 89, 2160 (1988). – Theoretical calculations of many doublet and quartet states in the visible and UV region.

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

Experiment Schematic Diagram of laser vaporization/OODR spectroscopy experimental setup

Optical-Optical Double Resonance Transition Scheme  Molecules are excited in two stages  from ground state to an intermediate state (B state) by dye laser  from intermediate state to the desired excited state (C state) by OPO laser  Molecules give out fluorescent photon and relax back to the ground state X2Σ+X2Σ+ B2Σ+B2Σ+ C2ΠC2Π Fixed laser pumping Scanning laser Detection: fluorescence dye laser OPO laser

Results & Discussion Low resolution LIF spectrum of YO 2 Π 3/2 2 Π 1/2 2Σ-2Σ- 2 Π 3/2 2 Π 1/2 4Σ-4Σ-

9 vibrational bands have been identified and studied B2Σ+B2Σ+ 2 Π 3/2 2 Π 1/2 4Σ-4Σ ( II )(I)(I)( III ) 33734

Detailed transition scheme for reaching the C 2 Π state via B 2 Σ + state Dye laser OPO laser

P(1.5), Q(1.5) and R(1.5) are observed  Ω’ = 0.5 X2Σ+X2Σ+ B2Σ+B2Σ+ [33.8] 2 Π 1/2 J 0.5 R 1 (0.5) R(1.5) Q(1.5) P(1.5) 0.5 OODR spectrum obtained by pumping R 1 (0.5) of B 2 Σ + - X 2 Σ + transition ( I ) [33.8] 2 Π 1/2 – B 2 Σ + transition Typical OODR spectrum of 2 Π – 2 Σ + transition

Assembled spectrum of [33.8] 2 Π 1/2 – B 2 Σ + transition

Confirmation of the Ω value ( Ω ’ = 1.5) --- First lines  Q(1.5) and R(1.5) lines are observed;  No P(1.5) line  Ω ’ = 1.5 ( II ) [33.9] 2 Π 3/2 – B 2 Σ + transition OODR spectrum obtained by pumping R 1 (0.5) of B 2 Σ + - X 2 Σ + transition X2Σ+X2Σ+ B2Σ+B2Σ+ [33.9] 2 Π 3/2 J 0.5 R 1 (0.5) R(1.5) Q(1.5)

The OODR spectrum indicates the upper state is a 4 Σ - state Analysis is still in progress

The OODR spectrum of the 4 Σ - - B 2 Σ - transition

High resolution spectrum [33.7] 4 Σ - – X 2 Σ + transition

Calculated electronic states of YO Langhoff et al Emission X2Σ+X2Σ+ A’ 2 Δ A2ΠA2Π B2Σ+B2Σ+ C2ΠC2Π a4Φa4Φ b4Πb4Π c4Σ+c4Σ+ e4Σ-e4Σ- Laser absorption Energy (cm -1 )

Molecular constants for the states of YO Upper stateT 0 (cm -1 )B (cm -1 )qr (Å) 2 Π 3/ Π 1/ Upper stateT 0 (cm -1 )B (cm -1 )γr (Å) 4Σ-4Σ

Summary 9 transition bands of YO have been studied by Optical- Optical Double Resonance Spectroscopy Spectroscopic properties of the 2 Π state have been determined to be: B = cm -1 r = Å Spin-orbit constant A = cm -1 A forbidden transition 4 Σ - - B 2 Σ + has been observed (further experimental work is needed for understanding this transition in detail) More work is necessary to characterize the observed states