E LECTRONIC T RANSITIONS OF S CANDIUM M ONOXIDE NA WANG, Y.W. NG, and A. S-C. CHEUNG The University...

ELECTRONIC TRANSITIONS

OF

SCANDIUM MONOXIDE

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 Spectroscopy69TH MEETING - JUNE 16-20, 2014

CONTENTS

Introduction

Experimental Setup

Results and Discussion

Summary

INTEREST IN STUDYING SCO

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: ns2(n-1)d1 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 4Σ as ground state. (L. Åkerlind et al (Arkiv. Fysic. 22, 41 (1962))

The ground state of ScO was confirmed to be X2Σ+ state which followed the unusual hyperfine coupling case bβS. The electronic transitions including A’2Δ – X2Σ+, A2Π – X2Σ+ and B2Σ+ - X2Σ+ transitions were obtained and analyzed successfully by many groups. A. Adams, W. Klemperer, T. M. Dunn (Can. J. Phys. 46 2213 (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))

PREVIOUS STUDIES ON SCO

EXPERIMENTAL SETUP FOR OODR SPECTROSCOPY

Schematic Diagram of Laser Vaporization/ OODR spectroscopy Experimental Setup

Sc rod

LIF/OODRtechniques

Laser Ablation/ReactionWith Free Jet Expansion

EXPERIMENTAL CONDITIONS

Molecular Production:

Sc + O2 (5% in Ar) ScO + etc.

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

Free Jet Expansion : i) backing pressure: 6 atm O2 (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

OPTICAL-OPTICAL DOUBLE RESONANCE TRANSITION SCHEME

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+

B2Σ+

C2Π

Fixed laserpumping

Scanning laser

Detection

RESULTS AND DISCUSSION

32500 33000 33500 34000 34500

Ω‘=1.5

[32.92] 1.5 - X2Σ+(1,0)(2,1)(0,0)

(2,0)

(b)

4Σ+ - X2Σ+(1,0)(0,0)[33.41] 0.5 - X2Σ+

wavenumber/cm-1

(1,1) (0,0) (1,0)

(a)

Ω‘=0.5

2Σ+

4Σ+

Low resolution broadband spectrum: (a) direct LIF spectroscopy, (b) OODR spectroscopy

Only v”=o can be observed for OODR spectrum

[32.85] 4∑+V1

0

[33.41] 0.5V1

0[32.92] 1.5 V

1

0

[33.36] 0.5 [33.37] 1.5 [33.39] 1.5[33.49] 1.5

[34.00] 2∑+ [34.01] 2∑+[34.15] 2∑+

B2∑+

X2∑+

626.2

cm-1

55

9.7

cm-1 51

1.3cm

-1

Pulsed Dye Laser

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, 2Σ+ and 4Σ+ states

(I) [33.4]0.5 – B2Σ+ transition

12830 12840 12850

Wavenumber/cm-1

R14

(1.5)Q14

(1.5)P14

(1.5)

OODR spectrum obtained by pumping R14(0.5)

P(1.5), Q(1.5) and R(1.5) are observed Ω’ = 0.5

X2Σ+ 0.5

B2Σ+

[33.4]0.5

1.5

0.5

1.5

2.5 J

R14(0.5)

R14

(1.5

)

Q14

(1.5

)

P14

(1.5

)

High resolution LIF spectrum of (0, 0) band of [33.4] 0.5 – X2Σ+ electronic state

33380 33390 33400 33410 33420

13.5

0.5

23.5

0.5

17.5 0.5

13.5 1.5

18.5

Q24

(J)

Q23

(J)Q

14(J)

Q13

(J)

R24

(J)

R23

(J)R

14(J)

R13

(J)

P24

(J)P

23(J)

P13

(J)

In

ten

sity

Wavenumber/cm-1

P14

(J)1.5

(II) [32.9]1.5 – B2Σ+ transitionOODR spectrum obtained by pumping R23(0.5)

Only P(1.5), and R(1.5) are observed Ω’ = 1.5

X2Σ+ 0.5

B2Σ+

[32.9]1.5

1.5

1.5

2.5 J

R23(0.5)

R23

(1.5

)

Q23

(1.5

)

12340 12345 12350 12355 12360

R23

(1.5)

Wavenumber/cm-1

Q23

(1.5)

(III) [34.1] 2Σ+ – B2Σ+ transition

X2Σ+ 6.5

B2Σ+

[34.1] 2Σ+

5.5

4.5

6.5 J

P14(6.5)

R14

(5.5

)

P14

(5.5

)

13580 13590

P14

(5.5)

R14

(5.5)

Wavenumber

OODR spectrum obtained by pumping P14 (6.5)

12270 12280 12290

TR41

(3.5)RQ31

(3.5)

PQ11

(3.5)

Wavenumber/cm-1

RP41

(3.5)

OODR spectrum obtained by pumping P14 (4.5) and P23(5.5) respectively

(IV) [32.85] 4Σ+ – B 2Σ+ transition

12270 12280 12290

PR12

(4.5)

RR32

(4.5)

RQ42

(4.5)

PP32

(4.5)

Wavenumber/cm-1

NP12

(4.5)

F4

F1

F3

F1F2

F1F2

F1F2

4

3

55.54.5

4.53.53.52.5

efefef

__

++__

N J

B 2Σ+

F1F2

F1F2

F1F25

4

43

32 3.5

4.5

5.55.5

4.5

3.5fe

fe

fe

+_

+_

_+

F1F22

1 2.52.5

fe

_+

PQ

11(3

.5)

PP

21(3

.5)

RR

21(3

.5)

NP

12(4

.5)

PQ

22(4

.5)

PR

12(4

.5)

N J

3.5

4.5

5.5

F3F4

F3F4

F3F4

5

5

67

6

4

5.5

4.5

3.5fe

fe

fe

_+

+_

+_

2.5 F3F44

32.5

fe

_+

RP

41(3

.5)

RQ

31(3

.5)

TR

41(3

.5)

PP

32(4

.5)

RQ

42(4

.5)

RR

32(4

.5)

N J

[32.8] 4Σ+

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

Molecular constants for observed upper states of ScO

Upper statev' νo B' q ro(Å) Remarks

[33.49] 1.5 0 33496.68 0.3788 0.0028 1.941[33.39] 1.5 0 33395.60 0.3599 - 1.992[33.37] 1.5 0 33372.82 0.3863 - 1.922 Perturbed[32.92] 1.5 1 33429.90 0.3552 - 2.005 Perturbed

  0 32918.64 0.4452 - 1.791           

[33.37] 0.5 0 33368.59 0.3036 - 2.168 Perturbed[33.41] 0.5 1 33971.30 0.4359 -0.0015 1.810

  0 33411.59 0.4367 - 1.808 Perturbed           

Upper state v' νo B' γ ro(Å)

[34.16] 2Σ+   34156.96 0.3957 0.0049 1.899[34.01] 2Σ+   34008.39 0.4190 -0.2898 1.846 Perturbed[34.00] 2Σ+   34001.56 0.4271 -0.3012 1.828 Perturbed

           Upper state v' νo B' γ λ ro(Å)

[32.85] 4Σ+ 1 33480.10 0.4125 1.07 0.16 1.860 Perturbed  0 32853.23 0.4382 1.03 0.53 1.805

(8σ)2(3π)4(9σ)1 X

2Σ+

(8σ)2(3π)4(1δ)1 A 2Δ

(8σ)2(3π)4(4π)1 A′ 2Π

(8σ)2(3π)4(10σ)1 B

2Σ+

Molecular Configuration Diagram of ScO molecule

(8σ)2(3π)3(9σ)1(1δ)1 2Πi(2), 4Πi

2Φi(2), 4Φi

(8σ)2(3π)3(9σ)1(4π)1 2Σ+(2), 4Σ+

, 2Σ-

(2)

4Σ-, 2Δ(2), 4Δi

(8σ)2(3π)3(9σ)1(10σ)1 2Πi(2), 4Πi

SUMMARYNew 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 4Σ+ – 2Σ+ forbidden transition was identified and studied.

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