A NEW 2Σ+ - 2Σ+ TRANSITION OF PtF BY INTRACAVITY LASER

ABSORPTION SPECTROSCOPYLEAH C O'BRIEN, TAYLOR DAHMS, KAITLIN A WOMACK

Department of Chemistry, Southern Illinois University Edwardsville, IL

JAMES J O'BRIENChemistry and Biochemistry, University of Missouri

St. Louis, MO

Previous Work on PtF• We reported ILS spectrum and analysis of the (0,0) and (1,0) bands of the [11.9] Ω=

3/2 - X 2Π3/2 transition of PtF

• J. Mol. Spectrosc. 265, 39-46 (2011)

• Bandheads at 11940 and 12496 cm-1

• Microwave spectrum by Okabayashi et al.

• J. Chem. Phys. 136, 174311 (2012)

• Several older theoretical calculations on the ground state

• High level ab initio calculations

• Relativistic calculations on the low-lying 2Π, 2Δ, and 2Σ states: Liu and Franke, J. Comp. Chem.

23, 564-575 (2002)

• PtF and HePtF calculations including relativistic effects: Zou, Liu, and Boggs, Dalton Trans. 39,

2023-2026 (2010).

Low-Lying States of PtF

• Ionic Molecule: Pt+(5d9)F–(2p6)

• ASO = -4200 cm-1

Without Spin-Orbit With Spin-Orbit

Te (eV) re (Å)

X 2Π3/2 0.000 1.873

Ω=1/2 0.106 1.8942Δ5/2 0.167 1.915

Te (eV) re (Å)2Σ 0.000 1.9212Π 0.252 1.9132Δ 0.462 1.942

Experimental Conditions• Conditions same as previous PtF work; recorded at the same time as

our previous work

• Produced in a Pt-lined hollow cathode plasma

• 0.35 to 0.60 Amp for discharge current

• ~1.6 Torr Argon support gas and trace amount of SF6

• Spectra recorded by Intracavity laser absorption spectroscopy, ILS

• Tg ranged from 100 – 130 μs, pathlength ranged from 0.92 – 1.2 km

• Calibration based on spectra from external I2 cell and Iodine Atlas

• Bandheads observed at 13078.9, 12523.4, and 11946.4 cm-1

Schematic of ILS Spectrometer

• ILS Absorption spectrum of PtF

Vibrational Assignments• Based on isotopologue structure, the band observed at 13078.9,

12523.4, and 11946.4 cm-1 were assigned as the (1,0), (0,0), and (0,1) bands, respectively.

• ΔG1/2′ = 555.5 cm-1

• ΔG1/2″ = 577.0 cm-1

• ILS Absorption spectrum of PtF

Rotational Analysis• Four branches were observed in both the (0,0) and (1,0)

bands

• Unusual spacing, considered 2Σ - X 2Π3/2

• Little overlap in J’s among the observed branches• Method of combination differences not workable

• Set aside for several years

• Fall 2013 contacted by Wenli Zou with new calculations

• He suggested it might be a specific 2Σ - 2Σ transition• Based on transition dipole moments, this is predicted to be strong

transition in the vicinity of our spectral features

Ω = 1/2 and 3/2 Electronic States of PtF

• Wenli Zou, unpublished work, 2013

(V) 2Σ+ – A 2Σ+ transition• No clear doublets → must have large γ values

• Try the Hougen method to estimate spin-rotation γ values (or λ-doubling p values) in Ω = ½ states of metal-halides with d9 electron configuration

• NiCl

• NiF

Predicted Atomic Energy Levels of a d9 MX

J.T. Hougen, J. Mol. Spectrosc. 267, 23–35. (2011)

Predicting γ-Value for A 2Σ+ State

• Determine crystal field parameters C0, C2, and C4

• Need energies for each 2Π, 2Σ, and 2Δ component: use data from Wenli

• Need ASO for Pt (5d96s1): known, ASO = -4210 cm-1

• Estimate β: β ~ 0.89, and optimize

• Solve system of linear equations (used Wolfram Alpha)

A β C0 C2 C4

-4210 cm-1 0.900 4082.8 613 341

Identify Term Energies of States Associated with d9 Electron Configuration

• One concern with applying Hougen method to PtF: low-lying quartet states may interfere with the X 2Π, A 2Σ+, and B 2Δ states and invalidate the Hougen analysis

Predicting γ-Value for A 2Σ+ State• Use A, β, C0, C2, and C4 to calculate 2θ

• 2θ = 4.85 rads

• p/2B = -2.7

• p = -1.48 cm-1

• γ = +2.02 cm-1

NiF

PGopher Simulation using Predicted Molecular Constants for the (V) 2Σ+ – A 2Σ+ Transition

12470 12475 12480 12485 12490 12495 12500 12505 12510 12515 12520 12525 12530 12535 12540 12545 12550 12555 12560Wavenumber/cm-1

Symmetry : :0/e :1/f

10

20

30

40

50

J

RfPf

Re

Pe

Rotational Analysis• Once we understood the spectrum, the analysis was straightforward

• Preliminary molecular constants are presented below

  E B D x 106 γ γD x 104

[12.5] 2Σ+, v=1 a + 13069.499(54) 0.2370(46) 9.3(23) 0.52(10) -9.5(33)[12.5] 2Σ+, v=0 a + 12511.695(49) 0.2426(46) 9.1(23) 0.50(10) -8.5(34)[12.5] 2Σ+, calc 13569 0.2444

A 2Σ+, v=0 a 0.2690(41) 9.2(23) 1.85(85) -7.9(32)A 2Σ+, calc 79. 0.2735 2.02

Summary• The (0,0) and (1,0) bands of a

new (V) 2Σ+ – A 2Σ+ transition have been analyzed

• Preliminary molecular constants obtained for both states

• Large values of γ

• High-level calculations from Wenli Zou very helpful

• Theoretical model from Jon Hougen invaluable

• Making progress on experimental observations of electronic structure of PtF

Potential Energy Curves for Ω= 1/2, 3/2, 5/2,7/2 and 9/2 states of PtF

Acknowledgements• Funding from NSF

• SIUE Students: Taylor Dahms and Kaitlin Womack

• UMSL STARS (High School) Students: Meredith Redick and Rebecca Steinberg

• Wenli Zou (post-doc at Southern Methodist U)

• Jon Hougen

• Thank you for your attention!

MO Diagram for PtF

• d9 electron configuration

• Low-lying 2Π, 2Σ, and 2Δ states

• One concern with Hougen method: low-lying quartet states of PtF may interfere with the X 2Π, A 2Σ+, and B 2Δ states and invalidate the Hougen analysis