A NEW 2 Σ Σ + TRANSITION OF PtF BY INTRACAVITY LASER ABSORPTION SPECTROSCOPY LEAH C O'BRIEN, TAYLOR DAHMS, KAITLIN A WOMACK Department of Chemistry, Southern Illinois University Edwardsville, IL JAMES J O'BRIEN Chemistry 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 2 Π 3/2 transition of PtF J. Mol. Spectrosc. 265, (2011) Bandheads at and cm -1 Microwave spectrum by Okabayashi et al. J. Chem. Phys. 136, (2012) Several older theoretical calculations on the ground state High level ab initio calculations Relativistic calculations on the low-lying 2 Π, 2 Δ, and 2 Σ states: Liu and Franke, J. Comp. Chem. 23, (2002) PtF and HePtF calculations including relativistic effects: Zou, Liu, and Boggs, Dalton Trans. 39, (2010).

Low-Lying States of PtF Ionic Molecule: Pt + (5d 9 )F – (2p 6 ) A SO = cm -1 Without Spin-Orbit With Spin-Orbit T e (eV)r e (Å) X 2 Π 3/ Ω=1/ Δ 5/ T e (eV)r e (Å) 2Σ2Σ Π2Π Δ2Δ

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 SF 6 Spectra recorded by Intracavity laser absorption spectroscopy, ILS T g ranged from 100 – 130 μs, pathlength ranged from 0.92 – 1.2 km Calibration based on spectra from external I 2 cell and Iodine Atlas Bandheads observed at , , and cm -1

Schematic of ILS Spectrometer

ILS Absorption spectrum of PtF

Vibrational Assignments Based on isotopologue structure, the band observed at , , and cm -1 were assigned as the (1,0), (0,0), and (0,1) bands, respectively. ΔG 1/2 ′ = cm -1 ΔG 1/2 ″ = 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 2 Σ - X 2 Π 3/2 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 2 Σ - 2 Σ 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Ω = 1/2 and 3/2 Electronic States of PtF Wenli Zou, unpublished work, 2013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) 2 Σ + – A 2 Σ + 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 d 9 electron configuration NiCl NiF Predicted Atomic Energy Levels of a d 9 MX J.T. Hougen, J. Mol. Spectrosc. 267, 23– 35. (2011)

Predicting γ-Value for A 2 Σ + State Determine crystal field parameters C 0, C 2, and C 4 Need energies for each 2 Π, 2 Σ, and 2 Δ component: use data from Wenli Need A SO for Pt (5d 9 6s 1 ): known, A SO = cm -1 Estimate β: β ~ 0.89, and optimize Solve system of linear equations (used Wolfram Alpha) AβC0C0 C2C2 C4C cm

Identify Term Energies of States Associated with d 9 Electron Configuration One concern with applying Hougen method to PtF: low-lying quartet states may interfere with the X 2 Π, A 2 Σ +, and B 2 Δ states and invalidate the Hougen analysis

Predicting γ-Value for A 2 Σ + State Use A, β, C 0, C 2, and C 4 to calculate 2θ 2θ = 4.85 rads p/2B = -2.7 p = cm -1 γ = cm -1 NiF

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

Rotational Analysis Once we understood the spectrum, the analysis was straightforward Preliminary molecular constants are presented below EBD x 10 6 γγ D x 10 4 [12.5] 2 Σ +, v=1a (54)0.2370(46)9.3(23)0.52(10)-9.5(33) [12.5] 2 Σ +, v=0a (49)0.2426(46)9.1(23)0.50(10)-8.5(34) [12.5] 2 Σ +, calc A 2 Σ +, v=0 a0.2690(41) 9.2(23) 1.85(85) -7.9(32) A 2 Σ +, calc

Summary The (0,0) and (1,0) bands of a new (V) 2 Σ + – A 2 Σ + 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 d 9 electron configuration Low-lying 2 Π, 2 Σ, and 2 Δ states One concern with Hougen method: low-lying quartet states of PtF may interfere with the X 2 Π, A 2 Σ +, and B 2 Δ states and invalidate the Hougen analysis