Post on 17-Jan-2016
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