Electronic transitions of Yttrium Monoxide

Allan S.-C. Cheung, Y. W. Ng, Na Wang and A. Clark

Department of ChemistryUniversity of Hong Kong

OSU International Symposium on Molecular Spectroscopy19 June, 2013 (WK11)

Paper: WK11

AcknowledgementsPh.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

IntroductionWhy 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)s2 nd1 model system for studying participation of d orbital Y has 5s2 4d1, Sc 4s2 3d1 and Zr 5s2 4d2 electronic configurations

S.R. Langhoff, et al, Annu. Rev. Phys. Chem. 39,  181 (1988)

IntroductionPrevious 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 - X2Σ+ transition in chemiluminescent reactions of YO.Observed weak C2Π - X2Σ+ 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.

B2Σ+ State re= 1.825 Å

A2Π State re= 1.793 Å

X2Σ+ State re= 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.

Gas-Phase YO Production Method

Laser ablation/reaction free jet expansionMolecule production:

Y + O2 (10% in Ar) → YO + etc.

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

Free Jet Expansion : i) backing pressure: 6 atm O2 (10% in Ar)

ii) background pressure: 1x10-5 Torr

OODR spectrum in the UV regionLaser system: Pulsed Dye laser &

Optical Parametric Oscillator laser

ExperimentSchematic 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+

B2Σ+

C2Π

Fixed laserpumping

Scanning laserDetection:fluorescence

dye laser

OPO laser

Results & Discussion Low resolution LIF spectrum of YO

2Π3/2

2Π1/2

2Σ-

33000 34000 35000

Wavenumber (cm-1)

2Π3/2

2Π1/2

4Σ-

9 vibrational bands have been identified and studied

3393433823

20741B2Σ+

2Π3/2 2Π1/2 4Σ-3384933787

333123324233147

33716

(II) (I) (III)

33734

Detailed transition scheme for reaching the C2Π state via B2Σ+ state

Dye laser

OPO laser

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

X2Σ+

B2Σ+

[33.8]2Π1/2J

0.5

R1(0.5)

1.5

1.52.5

R(1.5) Q(1.5)P(1.5)

0.5

OODR spectrum obtained by pumping R1(0.5) of B2Σ+ - X2Σ+ transition

13100 13110

P1(1.5)

Q1(1.5)

Wavenumber (cm-1)

R1(1.5)

33849 band

(I) [33.8]2Π1/2 – B2Σ+ transition

Typical OODR spectrum of 2Π – 2Σ+ transition

Assembled spectrum of [33.8]2Π1/2 – B2Σ+ transition

13100 13110

Wavenumber (cm-1)

8.5

7.5 1.5

8.5

8.5

1.5

8.5

1.5

1.5 8.51.51.5R

12(J)Q

12(J)

P12

(J)

R1(J)

Q1(J)

P1(J)

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]2Π3/2 – B2Σ+ transition

OODR spectrum obtained by pumping R1(0.5) of B2Σ+ - X2Σ+ transition

X2Σ+

B2Σ+

[33.9]2Π3/2 J

0.5

R1(0.5)

1.5

1.52.5

R(1.5)Q(1.5)

13190 13200

Q(1.5) R(1.5)

Wavenumber (cm-1)

33934 band

The OODR spectrum indicates the upper state is a 4Σ- state

Analysis is still in progress

12960 12980

Q2(6.5)

P2(6.5)

Wavenumber (cm-1)

Q2(6.5)

P2(6.5)

The OODR spectrum of the 4Σ- - B2Σ- transition

High resolution spectrum [33.7] 4Σ- – X2Σ+ transition

33700 33710

8.5

10.5

6.5

7.5

1.5

1.51.5

P2(J)

Q2(J)

Q1(J)

Wavenumber (cm-1)

R1(J)

2.5

Calculated electronic states of YO Langhoff et al

0

5000

10000

15000

20000

25000

30000

Em

issi

on

X2Σ+

A’2ΔA2Π

B2Σ+

C2Π

a4Φb4Πc4Σ+

e4Σ-

Las

er a

bsor

ptio

nEne

rgy

(cm

-1)

Molecular constants for the states of YO

Upper state T0 (cm-1) B (cm-1) q r (Å)2Π3/2 33934.21 0.3431 0 1.903

33823.48 0.2789 0 2.1112Π1/2 33849.00 0.3195 0.001 1.972

33786.65 0.2959 0 2.049

33311.79 0.2779 0 2.114

33241.75 0.3665 0 1.841

33146.90 0.3671 0 1.840

Upper state T0 (cm-1) B (cm-1) γ r (Å)4Σ- 33715.98 0.2921 0.640 2.062

33734.13 0.2921 0.574 2.062

Summary9 transition bands of YO have been studied by Optical-

Optical Double Resonance Spectroscopy

Spectroscopic properties of the 2Π 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 4Σ- - B2Σ+ has been observed (further experimental work is needed for understanding this transition in detail)

More work is necessary to characterize the observed states