Characterization of CaO+ and BaO+ by Two-Photon Ionization Spectroscopy Joshua H. Bartlett, Robert A. VanGundy, and Michael C. Heaven Department of Chemistry Emory University Atlanta GA 30322

69th International Symposium on Molecular Spectroscopy June 16-20, 2014

Emory University

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Why are we doing this? BaO has been studied. ●

Plenty of work has been done experimentally Several studies 1, 2, 3 exist studying the chemiluminescence of reactions of the form, Ba + NxOy → BaO* + NxOy-1

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Constants are reported from these studies with very high precision

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A synchrotron PES of BaO has recorded4 the IP at 6.46(7) eV

Not much work has been done theoretically ●

Typically included in papers to supplement experimental work

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1. RW Field et al., J. Chem. Phys . (1973) 2. Hedderith & Blom, J. Mol. Spec. (1990) 3. P. Bernath et al., J. Chem. Phys. (2005) 2 4. J. Dyke et al., J. Phys. Chem. A (1987)

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Why are we doing this? BaO has been studied. ●

None of the studies of BaO have been below 100 K ●

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Our spectra are jet-cooled to < 50 K

The IP error margin is on the order of hundreds of wavenumbers The value is suspect due to possible ionization from hot states ● Our error margin is on the order of wavenumbers ●

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No experimental work exists on the electronic structure of BaO + Once we find the IP, we can analyze the rovibronic structure with PFI-ZEKE

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Refining this information for the molecular ion is an important step towards a greater degree of control in molecular ion trapping experiments

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Why are we doing this? CaO has been studied. ●

Some work has been done experimentally ●

Emission studies were done with a Ca hollow cathode source

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A synchrotron PES of CaO has recorded the IP at 7.6(5) eV 6

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Results from a guided ion beam study indirectly determined the IP at 6.66(18) eV 7

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Plenty of work has been done theoretically Harrison et. al.8 did an RCCSD(T) examination of MX (M = Ca, Zn; X= O, F) and predicted many properties

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Studies have been done up to the MRCI+Q 9 level

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5. A. Lagerqvist et al., Proc. Phys. Soc. (1950) 6. E. Murad, J. Chem. Phys. (1983) 7. NF Dalleska & PB Armentrout, Int. J. Mass Spec (1994) 8. JF Harrison et al., ACS Symposium Series (2002)

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Why are we doing this? CaO has been studied. ●

Previous experimental studies are at high temperature ●

●

Our jet-cooled apparatus provides advantages

CaO+ is an interesting molecule The ground state is 2Π with a low-lying 2Σ+ state 8, 9 ● The IP discrepancy can be laid to rest ● Only theoretical work exists on the electronic structure so far ●

Like BaO, CaO is a molecule that can be produced easily after atomic ion trapping in Coulomb crystals, and has potential for further study; knowledge of the quantum states is useful

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8. JF Harrison et al., ACS Symposium Series (2002) 9. H Khalil et al., J. Phys. Chem. A 5 (2013)

Experimental Setup for jet-cooled metal oxides Microchannel plates Photomultiplier Ba/Ca rod

Drift tube

Gate valve Skimmer

Pulse valve Charged plates

O2/He (~1%-2%, 40-50 psi) Microchannel plates

Diffusion pump (10-6 torr) Emory University

Turbomolecular pump (10-8 torr) 6

Experimental Setup: Nd:YAG lasers everywhere TOFMS-PIE LIF Lambda-Physik ScanMate Pro 355nm or 532nm pumped pulsed dye laser PFI-ZEKE

Continuum ND6000 532nm or 355nm pumped pulsed dye laser

Continuum Minilite 1064nm output

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BaO A1Σ+ ← X1Σ+ Laser-induced fluorescence v= 0

16500

3

17000

17500

18000

4

18500

5

19000

6

19500

7

20000

-1

Photon Energy (cm )

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BaO A1Σ+ ← X1Σ+ Laser-induced fluorescence

B”= 0.312614 cm-1 B'= 0.271195 cm-1 (4,0) A-X (3,0) Experiment Simulation T = 35 K

19160

19165

19170

19175

19180

19185

-1

Photon Energy (cm )

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CM Western, pgopher, University9of Bristol, 2007

BaO A1Σ+ ← X1Σ+ Laser-induced fluorescence State

Molecular constants obtained from fit parameters Constant Energy

X1Σ+

0 cm-1 Be

0.313 cm-1

ωe

669.74 cm-1

ωexe

2.019 cm-1

A1Σ+

3 3

3

16722.25 cm-1

3

B0,3,4,5,6,7

0.2583, 0.255(3), 0.271(3), 0.271(3), 0.269(3), 0.256(3)cm -1

ωe

499.5(9) cm-1

ωexe

1.4(1) cm-1

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3. P. Bernath et al., J. Chem. Phys. 10 (2005)

Ionizing BaO Resonance-enhanced multi-photon ionization: TOFMS 138

138

+

BaO

+

Ion Current

Ba

134

135

136

137

137

+

BaO

hν total = 53277.5 (field-corrected) -1

(A-X (4,0) R-branch band head)

-1

(nonresonant, ionizing)

18697.9 cm

34482.8 cm

11.0

11.1

11.2

11.3

11.4

11.5

11.6

11.7

11.8

Time of Flight (µ s)

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11.9

Ionizing BaO Resonance-enhanced multi-photon ionization: Photoionization efficiency

First photon = 19183.3 cm

-1

138

BaO Current

A-X (5,0) band head

35100

35200

35300

35400

35500

35600

35700 -1

Second Photon Energy (cm )

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35800

35900

36000

12

Ionizing BaO Resonance-enhanced multi-photon ionization: Photoionization efficiency

First photon = 19183.3 cm

-1

The spectrum is dominated by one-color twophoton ionization!

138

BaO Current

A-X (5,0) band head

35100

35200

35300

35400

35500

35600

35700 -1

Second Photon Energy (cm )

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35800

35900

36000

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Ionizing BaO : finding the IP

-1

Second Photon Energy (cm )

BaO Current

35666.7

35676.7

hν 2

35686.7

35696.7

35706.7

54980

54990

-1

138

hν 2 + 19183.3 cm

54950

54960

54970

-1

Two-Photon Energy (cm ) (field-corrected)

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ZEKEs from BaO+

ZEKE Signal

Two-photon PFI-ZEKE

-1

0.60 V cm

-1

0.14 V cm

54950

54960

54970

54980

-1

Two-Photon Energy (cm )

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54990

55000

15

CASSCF/MRCI/SO for BaO+ 12000 11000

Ba: ECP46MWB, aug-cc-VTZ O: aug-cc-VTZ

10000 9000 8000

2

XΣ

-1

Energy (cm )

7000

+

6000 5000 4000 3000

2

AΠ

2000

3/2, 1/2

1000 0 2.0

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2.2

R (Ang.)

2.4

2.6

H-J Werner et al., MOLPRO, version 16 2010.1

CASSCF/MRCI/SO for BaO+ 12000 11000

Ba: ECP46MWB, aug-cc-VTZ O: aug-cc-VTZ

10000 9000 8000

2

XΣ

-1

Energy (cm )

7000

+

A2Π1/2 = 1247.4 cm-1

6000 5000

A2Π3/2 = 1141.9 cm-1

4000 3000

2

AΠ

2000

3/2, 1/2

1000 0 2.0

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2.2

R (Ang.)

2.4

2.6

H-J Werner et al., MOLPRO, version 17 2010.1

BaO+ results so far Two-photon PFI-ZEKE

X2Σ+

IP = 54986(3) cm-1 ΔG1/2

536(3) cm-1 IP = 55600(300) cm-1

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18 4. J. Dyke et al., J. Phys. Chem. A (1987)

BaO+ results so far Two-photon PFI-ZEKE

X2Σ+

IP = 54986(3) cm-1 ΔG1/2

536(3) cm-1 IP = 55600(300) cm-1

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More to come...

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19 4. J. Dyke et al., J. Phys. Chem. A (1987)

CaO C1Σ+ ← X1Σ+ Laser-induced fluorescence

v=

29250

1

29400

29550

29700

2

29850

3

30000 -1

30150

30300

30450

Photon Energy (cm )

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TOFMS from the CaO source +

Ca2O

Ion Current

Multi-photon ionization: TOFMS

hv1 = 22000.0 cm

-1

-1

hv2 = 32921.8 cm

+

+

CaO

+

Ca3O2

Ca

5.0

7.5

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10.0

12.5

+

Ca4O3

+

Ca5O4

+

Ca6O5

15.0

17.5

Time of Flight (µ s)

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PIE results so far with CaO Multi-photon ionization: PIE

+

CaO Current

IP < 54550 cm-1

54540

54550

54560

-1

54570

54580

Two-Photon Energy (cm ) (field-corrected)

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PEC for CaO+ CASSCF potential-energy curves of the low-lying electronic states of CaO (in black), CaO+ (doublets are in red and quartets are in blue), and CaO− (doublets in red).9 State

Constant

Energy (cm-1)

X2Π

IP

54753.7

ωe

639.3

ΔESO

127.4

Te

564.6

ωe

703.2

A2Σ+

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9. H Khalil et al., J. Phys. Chem. A (2013)

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Goals for the foreseeable future Improve source conditions (?) Ablation production of CaO ● New BaO rod ● Long-term BaO production ●

Conclude BaO+ PFI-ZEKE ● Higher energy bands (including A state) ● Rotational resolution ● Extend theoretical work ●

Find CaO IP PIE followed by PFI-ZEKE ● Can compare to existing theory ● Investigate Ca O production (?) n n-1 ●

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Acknowledgments The Heaven group Dr. Michael Heaven Dr. Adrian Gardner Dr. Jacob Stewart Dr. Jiande Han Robert VanGundy Michael Sullivan Kyle Mascaritolo $$$$$$$$$ US Department of Energy Office of Naval Research

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Acknowledgments The Heaven group Dr. Michael Heaven Dr. Adrian Gardner Dr. Jacob Stewart Dr. Jiande Han Robert VanGundy Michael Sullivan Kyle Mascaritolo

Thank you!

$$$$$$$$$ US Department of Energy Office of Naval Research

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