Columbus, June 2008.ppt Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Zentrum für Festkörperchemie & Neue Materialien The Salt Molecule

Columbus, June 2008

<Dateiname>.ppt

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Zentrum für Festkörperchemie

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The Salt Molecule LiKF2

Richard MawhorterDepartment of Physics & Astronomy, Pomona CollegeJens-Uwe Grabow Institut für Physikalische Chemie. GWLU Hannover

LiKF2

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Columbus, June 2008 <Dateiname>.ppt


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alkali halides in the gas phase

Introduction, M2X2 Salt – Alkali Halide Gas Phase Molecules

Laser Ablation & Mixed Salt Kinetics

Experimental, LiKF2

Electron DiffractionMicrowave Spectroscopy

ResultsSpectroscopic Parameters, IsotopologuesStructure

Outlook, M’M’’X’X’’

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alkali halide vapor

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1/r2 force toform monomers,

1/r3 force to form dimers

=>

much stronger than ~1/r6 forces for metal cluster formation

Mixed Dimer Formation

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electron diffraction

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COBRA chamber

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production of Non-volatile Species:Coaxial Ablation Twin Source (CATS)

(precursor) / rare gas

Nd:YAG LASER I

Nd:YAG LASER II

supersonicexpansion

rotating/translating rods: elements, alloys, compoundsbulk material, compressed powder

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6LiF/KF Rods: before & after ablation

Laser Ablation Source:

Top view

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Spherical Reflector: Transmit & Receive Antennae

supersonic-jet source

high-frequency antennae

low-frequency antennae

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LiKF2 moments of inertia

a

bc

xF (fixed by IA)

yF (fixed by c.m. & IB)

yK (fixed by c.m. & IB/IC)

fixed by c.m. & IC

Simplest case:

IA = 2(mFxF2)

asymmetric top: A > B > C

planarity: IC = IA + IB

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Microwave spectroscopy of mixed alkali halide dimers: LiNaF2, S. Biermann, J. Hoeft,T. Törring, R. Mawhorter, F.J. Lovas, R.D. Suenram, Y. Kawashima, E. Hirota, J. Chem. Phys. 105 9754 (1996).analyzed lines (cm & mm wave): 49 6LiNaF2 & 46 7LiNaF2

LiNaF2

LiNaF2 spectroscopic constants

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Mixed alkali halyde dimers:LiNaF2-rods with varying NaF/LiF mole fractions

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Mixing Salt

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LiNaF2:NaF Number Density vs. LiF Mole Fraction

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Mole Fraction LiF in NaF

LiN

aF2:

NaF

Rat

io

Series1

LiNaF2:NaF Ratio vs. LiF Mole Fraction

Peak ~15%

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simple kinetic model for LiF/NaF formation

Assumptions:

•LiF more likely to dimerize

•Dimerization quickly quenched

Peak ~15%

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6Li39KF2 r0 Structure

A=6475.984(16) MHz

B=5590.410(19) MHz

C=2994.110(12) MHz

r0(Li-F)= 1.697Å/1.701Å

r0(K-F)= 2.394Å/2.397Å

A=6477.34(45) MHz

B=5409.892(73) MHz

C=2941.932(51) MHz

3 Isotopologues

6Li39KF2 (8 lines)7Li39KF2 (5 lines)6Li41KF2 (2 lines)

Θ(F-Li-F) = 115.25° / Θ(F-Li-F)QZ = 115.28°

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LiKF2

LiNaF2

???

LiCsF2

ED homo-dimer geometries

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Do mixed dimers relate to regular dimers?

One model: Mixed dimers consist of 2 regular half-dimers:Asymmetric M-F-N angle ≈ average of M-F-M and N-F-N angles

for Θ(Li-F-Na)=82.9°, average(Li-F-Li/Na-F-Na) = 82.7°√reasonably good agreement however:for LiKF2, Θ(Li-F-K)=85.8°, average(Li-F-Li/K-F-K) = 87.8°

Agreement not as good

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Further results

Centrifugal Distortion Constants

DJ= -.026(3) MHzDJK= .113(13) MHzDK= -.089(10) MHz

inonic clusters are less rigid than covalent species

Nuclear Hyperfine Structure due to interaction of the 39K nuclear quadrupole moment

3/2 χaa = -5.2 MHz¼ (χbb – χcc) = -1.8 MHz

Additional splittings observed from 7Li nuclear quadrupole moment

MP2/QZ predictions give excellent agreement with observed splittings and predicted dipole moment of μ = 4.25 D is consitent with observation

Nuclear quadrupole coupling tensor principle axes

Kernquadrupolkopplungstensorhauptachsensystem

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Future Work

Mixed Alkali Halide Dimers with only 1 Q≠0 Nucleus

• 6LiNaF2 – first molecule observed

•6Li39KF2 , 6Li41KF2 - this study

• 6LiRbF2, 6LiCsF2 – next in line; CsF very hygroscopic, but Cs challenging

• 6Li2FCl , 6Li2FBr, 6Li2FI – involve Cl, Br, I; too light to see LiX to tune => mix in few % NaCl, also helps in making sample rods

Asymmetric MixedDimer: LiNaFCl

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acknowledgement

Colin Pulham, EdinburgPhilip Camp, EdinburgPhil McCaffrey, Edinburg

electrical shop mechanical shop

Deutsche Forschungs-Gemeinschaft (DFG)

Land Niedersachsen

Deutscher Akademischer Austauschdienst (DAAD)

Mellon Foundation

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+ -

Figures from:Rohlf Modern Physics from α to Z0

Ionic Bond Dipole Dipoles Attract

Dimer Molecule

(SmallestCluster/Nanoparticle)

Bulk, Dimer, Monomer

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Coaxial oriented Beam-Resonator Arrangement (COBRA)

t

E

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6LiKF2: 39K–hyperfine structure

Documents

Columbus, June 2008.ppt Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Zentrum für Festkörperchemie & Neue Materialien The Salt Molecule