1. 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

2. 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

3. 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)

4. 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 = 1.825 Å A 2 Π Stater e = 1.793 Å X 2 Σ + Stater e = 1.788 Å Langhoff et al., J. Chem. Phys. 89, 2160 (1988). – Theoretical calculations of many doublet and quartet states in the visible and UV region.

5. 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

6. Experiment Schematic Diagram of laser vaporization/OODR spectroscopy experimental setup

7. 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

8. 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. 9 vibrational bands have been identified and studied 33934 33823 20741 B2Σ+B2Σ+ 2 Π 3/2 2 Π 1/2 4Σ-4Σ- 33849 33787 33312 33242 33147 33716 ( II )(I)(I)( III ) 33734

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

11. 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) 1.5 2.5 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

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

13. 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) 1.5 2.5 R(1.5) Q(1.5)

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

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

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

17. 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 )

18. Molecular constants for the states of YO Upper stateT 0 (cm -1 )B (cm -1 )qr (Å) 2 Π 3/2 33934.210.343101.903 33823.480.278902.111 2 Π 1/2 33849.000.31950.0011.972 33786.650.295902.049 33311.790.277902.114 33241.750.366501.841 33146.900.367101.840 Upper stateT 0 (cm -1 )B (cm -1 )γr (Å) 4Σ-4Σ- 33715.980.29210.6402.062 33734.130.29210.5742.062

19. 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 = 0.3665 cm -1 r = 1.840 Å Spin-orbit constant A = 692.46 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