E LECTRONIC T RANSITIONS OF S CANDIUM M ONOXIDE NA WANG, Y.W. NG, and A. S-C. CHEUNG The University of Hong Kong 109 Pokfulam Road, Hong Kong SAR, P.R.China International Symposium on Molecular Spectroscopy 69TH MEETING - JUNE 16-20, 2014

C ONTENTS Introduction Experimental Setup Results and Discussion Summary

I NTEREST IN S TUDYING S C O Astrophysics ScO has been found in the spectra of M-type stars, where its spectrum usually accompanies those of TiO Merrill et al (Astrophys. J. 136, 21 (1962)) Catalysis Scandium oxide is a good catalyst for selective catalytic reduction of nitric oxide with methane. Fokema et al (applied catalysis B. 18, 71 (1998)) Spectroscopic interest Sc atom: ns 2 (n-1)d 1 with only one electron in the d orbital Molecular and electronic structure of Sc diatomic molecule.

Theoretical studies by using different calculation methods for ground state and low- lying electronic states of ScO had been done. K. D. Carlson, E. Ludena, C. Moser (J. Chem. Phys. 43, 2408 (1965)) D. W. Green (J. Phys. Chem. 75, 3103 (1971)) Bauschlicher Jr., S. R. Langhoff (J. Chem. Phys. 85, 5936 (1986)) G. H. Jeung, J. Koutecky (J. Chem. Phys. 88, 3747 (1988)) S. M. Mattar (J. Phys. Chem. 97, 3171 (1993)) Experimental Work: L. Åkerlind et al observed the spectrum of ScO for the first time and consider 4 Σ as ground state. (L. Åkerlind et al (Arkiv. Fysic. 22, 41 (1962)) The ground state of ScO was confirmed to be X 2 Σ + state which followed the unusual hyperfine coupling case b βS. The electronic transitions including A’ 2 Δ – X 2 Σ +, A 2 Π – X 2 Σ + and B 2 Σ + - X 2 Σ + transitions were obtained and analyzed successfully by many groups. A. Adams, W. Klemperer, T. M. Dunn (Can. J. Phys (1968)) C. L. Chalek, J. L. Gole (J. Chem. Phys. 65, 2845 (1976)) P. K. Schenck, W. G. Mallard, J. C. Travis, K. C. Smyth (J. Chem. Phys. 69, 5147 (1978)) W. J. Childs, T. C. Steimle (J. Chem. Phys. 88, 6168 (1988)) S. F. Rice, W. J. Childs, R. W. Field (J. Mol. Spectros. 133, 22 (1989)) J. Shirley, C. Scurlock, T. Steimle (J. Chem. Phys. 93, 1568 (1990)) L. B. Knight Jr., J. G. Kaup, B. Petzoldt, R. Ayyad, T. K. Ghanty, E. R. Davidson(J. Chem. Phys. 110, 565 ( 1999)) S. Mukund, S. Yarlagadda, S. Bhattacharyya, S. G. Nakhate(J. Quantitative Spectroscopy & Radiative Transfer, 113, 2004 (2012)) P REVIOUS S TUDIES ON S C O

E XPERIMENTAL S ETUP FOR OODR SPECTROSCOPY Schematic Diagram of Laser Vaporization/ OODR spectroscopy Experimental Setup Sc rod LIF/OODR techniques Laser Ablation/Reaction With Free Jet Expansion

E XPERIMENTAL C ONDITIONS Molecular Production: Sc + O 2 (5% in Ar) ScO + etc. Ablation Laser : Nd:YAG, 10Hz, 532nm, 5mJ Free Jet Expansion : i) backing pressure: 6 atm O 2 (5% in Ar) ii) background pressure: 1x10 -5 Torr LIF spectrum in the UV region (290 ~ 311nm) OODR spectrum in Visible and Infrared region (720 ~ 815nm) Laser systems: Pulsed Dye laser & Optical Parametric Oscillator laser

O PTICAL -O PTICAL D OUBLE R ESONANCE T RANSITION S CHEME ScO 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

R ESULTS AND D ISCUSSION

Low resolution broadband spectrum: (a) direct LIF spectroscopy, (b) OODR spectroscopy Only v”=o can be observed for OODR spectrum

13 electronic transitions have been recorded and analyzed There are four different types of electronic states have been identified: Ω’ = 0.5, Ω’ = 1.5, 2 Σ + and 4 Σ + states

(I) [33.4]0.5 – B 2 Σ + transition OODR spectrum obtained by pumping R 14 (0.5) P(1.5), Q(1.5) and R(1.5) are observed Ω’ = 0.5 X2Σ+X2Σ+ 0.5 B2Σ+B2Σ+ [33.4] J R 14 (0.5) R 14 (1.5)Q 14 (1.5)P 14 (1.5)

High resolution LIF spectrum of (0, 0) band of [33.4] 0.5 – X 2 Σ + electronic state

(II) [32.9]1.5 – B 2 Σ + transition OODR spectrum obtained by pumping R 23 (0.5) Only P(1.5), and R(1.5) are observed Ω’ = 1.5 X2Σ+X2Σ+ 0.5 B2Σ+B2Σ+ [32.9] J R 23 (0.5) R 23 (1.5)Q 23 (1.5)

(III) [34.1] 2 Σ + – B 2 Σ + transition X2Σ+X2Σ+ 6.5 B2Σ+B2Σ+ [34.1] 2 Σ J P 14 (6.5) R 14 (5.5)P 14 (5.5) OODR spectrum obtained by pumping P 14 (6.5)

OODR spectrum obtained by pumping P 14 (4.5) and P23(5.5) respectively (IV) [32.85] 4 Σ + – B 2 Σ + transition F4F4 F1F1 F3F3

Energy level diagram for the 4 Σ + – 2 Σ + transition

Molecular constants for observed upper states of ScO Upper state v'νoνo B'qr o (Å)Remarks [33.49] [33.39] [33.37] Perturbed [32.92] Perturbed [33.37] Perturbed [33.41] Perturbed Upper statev'νoνo B'γr o (Å) [34.16] 2 Σ [34.01] 2 Σ Perturbed [34.00] 2 Σ Perturbed Upper statev'νoνo B'γλr o (Å) [32.85] 4 Σ Perturbed

(8σ) 2 (3π) 4 (9σ) 1 X 2 Σ + (8σ) 2 (3π) 4 (1δ) 1 A 2 Δ (8σ) 2 (3π) 4 (4π) 1 A′ 2 Π (8σ) 2 (3π) 4 (10σ) 1 B 2 Σ + Molecular Configuration Diagram of ScO molecule (8σ) 2 (3π) 3 (9σ) 1 (1δ) 1 2 Π i (2), 4 Π i 2 Φ i (2), 4 Φ i (8σ) 2 (3π) 3 (9σ) 1 (4π) 1 2 Σ + (2), 4 Σ +, 2 Σ - (2) 4 Σ -, 2 Δ(2), 4 Δ i (8σ) 2 (3π) 3 (9σ) 1 (10σ) 1 2 Π i (2), 4 Π i

S UMMARY New electronic states of ScO in the high energy region have been studied using LIF and OODR Spectroscopy. Thirteen vibronic transition bands were observed and analyzed. Accurate molecular constants were determined. A 4 Σ + – 2 Σ + forbidden transition was identified and studied.